Batteries Not Included, or Required, for These Smart Home Sensors
Comments
xoa
dn3500
Children too. My own hearing extended to about 23 kHz until I was in my early 20s, and I don't think I was exceptional. There was a jewelry store in my town that I couldn't go in to because the "ultrasonic" motion detector was so painfully loud. But I doubt these devices would be a problem for children or pets because the pulse is so short.
simpleintheory
Are you sure it wasn’t one of these? https://en.wikipedia.org/wiki/The_Mosquito
dn3500
Yes. This was more than 50 years ago. The store owner let me examine the device. It was wired into his alarm system. It even had the frequency listed on the label.
pavel_lishin
My hearing is still keen enough that when I'm biking around, I avoid certain streets because those houses have anti-rodent ultrasonic systems that hurt my ears.
madaxe_again
I mean, TV. Kids were definitely a market for it, throughout its history, but until the flat panel era nobody cared that the flyback transformer in most CRTs made a deafening whine in the 20khz range. I could walk into a house and hear a soundless TV three rooms away, and I know I wasn’t alone in that.
invalidSyntax
Yeah I could too(not know though...). Trying to sleep, and knowing your parents are watching TV in the living room few doors away isn't the best experience.
ZaoLahma
From the article:
> And they don’t travel very far, so only nearby microphones would “hear” the tag. That makes the devices inherently private, Deng said, because other people wouldn’t detect any activity unless they were within a meter or so.
It would seem these things don't really produce loud noises, so probably not adding much to the noise pollution that already exists in our environments. At the same time it seems the statement kind of negates the "point" of this tech, that you don't need an active (energy consuming) device close to the source of the events that you want to detect. So not sure of how to interpret it.
fleventynine
PoE is lousy for sensors. The switch will cut the power if you draw less than 10mA (480 mW), so regardless of PHY efficiency (which is terrible compared to most RS-485, CAN, or even radio ICs), you are REQUIRED by the spec to generate heat that will mess up your sensor measurements.
xoa
>The switch will cut the power if you draw less than 10mA (480 mW), so regardless of PHY efficiency [...] you are REQUIRED by the spec to generate heat that will mess up your sensor measurements.
Out of genuine curiosity, could you elaborate on this further, or share some sources I could read more on? I knew that was once the case, but my understanding was that significant improvements were made for the Maintain Power Signature (MPS) requirements with dual signature and PD standards in the 802.3bt update. According to [0], in the section on 145.3.9 PD MPS:
>"To further reduce minimum standby power consumption for PoE systems, Type 3 and Type 4 dual-signature PDs can make use of optimized MPS timings when connected to a Type 3 or Type 4 PSE, as shown in Figure 19. PDs assigned to Class 1 through 5 must draw a current of 10 mA for at least 7 ms with no more than 310 ms between pulses. This translates to an average power consumption of 12 mW per pairset, or about 1/10th (12 mW/ 124.6 mW ) of the Type 1 / Type 2 minimum pulse average power consumption."
So my assumption was that the spec had significantly improved on this front starting around 7 years ago? I mean, I'm aware that there can be a very, very great deal of lag time between specs and sufficiently cheap and developed new chipsets taking advantage, but I don't think that's the spec's fault either. In principle if the market was there (and yes, it isn't) the tech could meet it right? My extremely limited experience too is that typical wireless battery powered setups can be sensitive to heat as well in the few applications I've dealt with where it's significant, which makes me wonder if in practice in some cases it might be better to use an IR sensor aimed at a semi-closed or closed but air separated material with known (presumably as close to 1.00 as feasible?) thermal emissivity.
Still, there's lots of sensor use cases where it just doesn't matter, but it'd be nice to be able to hard wire+network on the cheap stuff that's very isolated from wireless signal and physically awkward to get at. I'm fully cognizant though that it's a dream unlikely to be realized, just a personal wish there was more PoE IOT stuff (and while we're at it with magical dream lands that it all had open fully local APIs and everyone worked on first class Home Assistant support and...).
----
0: https://ethernetalliance.org/wp-content/uploads/2019/08/EA_P...
fleventynine
Good luck finding reasonably priced switches and low power PD ICs that support type 3 or type 4 PoE.
Also, supporting those tiny pulses requires large capacitors to hold a charge in between pulses. That plus the required magnetics make PoE sensors way more bulky and expensive to manufacture than old fashioned RS-485 sensors.
tomaskafka
I think we already established "eff anyone sharing the planet with us that's not us" the moment we made acoustic underwater sonars that make life hell for any whale or dolphin in 100 km range, so this is keeping that approach ...
nick238
Why would this be any different from dropping a coin or other small metal object? If you're worried about ultrasonic noise pollution, nearly every SMPS operates there, and they're constantly running.
mmmlinux
Out of curiosity what do you find missing from the PoE sensor market?
xoa
>Out of curiosity what do you find missing from the PoE sensor market?
I'd be unironically delighted if you could point me at some site helping me find what I've been missing like a goof, because it feels more like the question is "what isn't missing from the PoE sensor market?" It's pretty niche isn't it, with what little there is available also being at enormously increased prices? Take something as simple as "is there water where it shouldn't be", isn't there basically just the Aquo Proteus XE at $350 and, I think maybe one other I can't remember? Surely there are some "call us for a quote" industrial gear too but it's not exactly the common case vs z-wave/zigbee/wifi. Same with pretty much whatever else one might name. Like, what if you want a semi-permanent motion sensor (not a camera), are there any PoE options at all? I think I remember reading someone working on an mmWave one to get it work with HA but that's it. And yes 100% you can say that it's "overkill" or the like but looking at DigiKey's PoE controller pricing doesn't seem like it inherently has to be a huge premium, just isn't anything mass produced.
I mean, it is certainly very arguable that the entire IOT market is and always has been sort of a total mess more than not, and that PoE switches weren't the $50/8-port affairs you can get now either until pretty recently. I totally understand why it's not a thing, I want to be clear this is more of an idle wistful "that'd be a nicer world" along with all sorts of other areas of tech. And I know there are PoE splitters so sometimes you can get roughly the same effect if something has ethernet+power separately. Wireless is also certainly sometimes simply the most sensible option. Just would be nice to have more options when it counted is all. I've dealt with enough odd spaces where it's a pain to get any signal in and even if it's only once every few years it still sucks to have to have somebody work their way in there to replace a battery and sometimes things randomly fritz out, makes one long for good ol' hard wire with super easy ways to just power cycle the switch and eliminate lots of complicated stacks of networking. Ah well.
haddonist
https://shop.everythingsmart.io/products/everything-presence...
"Everything Presence Pro is our most advanced presence sensor ever, combining long-range static mmWave, tracking mmWave, PIR, PoE, Ethernet/WiFi connectivity, and optional CO₂ sensing (Sold separately) in a single, ultra-capable device"
USD$93.00
---
https://apolloautomation.com/products/r-pro-1?_pos=1&_sid=f8...
Apollo Automation "R PRO-1 PoE dual mmWave Multisensor (LD2450 | additional LD2412 optional)"
- Dual mmWave Compatibility: LD2412 and LD2450 - TR390 for ambient lux and UV sensing - Optional SCD40 for high-accuracy NDIR CO₂ sensing (extra $20)
USD$69.99
---
Also check out https://www.tindie.com/ - it's a site for small companies & individuals to sell tech-related stuff. A quick POE search turned up Radiation Dosimeters, Air quality meters, BLE gateways and more.
ssl-3
I like PoE, too -- ethernet in general is something that I think is pretty swell.
But most people are not like us. They're not interested in wires, and many have grown up in a very connected world where there aren't any wires.
Smart home sensors are already a pretty niche market. People who want smart home devices that use ethernet are a small subset of that niche. By the time we drill down to smarthome stuff that is powered with ethernet, we've lost almost everyone's attention.
...
That said, I've made dumber things than this work. A facility I've done work at has a physical access control system that is "wireless". It's not really wireless, of course; it's got a fuckton of wire, but the comms are at least wireless.
They wanted a pushbutton on their dispatch console's touch screen that could unlock the front door. Easy-enough, right? The console provides contact closures on the back end.
But the "wireless" access control system's only useful interface for this was a stupid key fob, like for a car. It uses a CR2032 battery. It was, again, stupid. I hated it, but I used it anyway.
I powered it with 12VDC that was stepped down with a fixed 3-volt linear regulator. I used some rather nice Japanese-made small-signal relays to "push" the buttons on the fob. Those little relays were, in-turn, controlled by the operation of the dispatch console's relays (which were located a couple of hundred hundred cable-feet away).
It took a couple of hours to put it together. They paid the bill. It's been working fine for years.
Am4TIfIsER0ppos
If they are anything like the ultrasonic pest devices people can hear them. I can hear those. I can hear the one a neighbor has near a chicken enclosure every time I walk past on the street.
harg
There already exists "kinetic" switches for lights etc whose switch contains some passive electronics that when actuated produces enough energy to emit a radio signal that can be read by a relay module. They're pretty handy as you can basically place the switch anywhere you want without the need for the wires to be there. The relay can live in the light fitting or somewhere else convenient.
There's probably no reason why these kinetic switches can't also be used for detecting other events like doors opening/closing etc. I feel like a radio signal is a bit more reliable and easier to detect than high frequency sound.
I also think calling these a "sensor" is a bit of a stretch. They detect events but have no knowledge of the current state of the thing they're sensing. E.g. the can detect a door opening/closing, but have no idea if the door is open or closed at a given time
buescher
Piezo harvesting switches and similar (I think there’s a flywheel design out there too) are quite expensive, not terribly reliable or consistent, and require substantial activation force. Conventional switches and batteries that can last for years in remote push buttons and sensors are extremely inexpensive in volume.
taco_emoji
The ones I have in my house [0] were not that expensive and have been quite reliable for years now.
ranger_danger
Do you know of any where the receiver plugs into an existing outlet and has an inline receptacle for the controlling device already wired up?
taco_emoji
No, but the one I linked could be wired up that way with a pigtail plug & receptacle, although it'd be pretty big and unwieldy.
nkohari
That's not really true. We've used these for years to control our Hue lights, and they're fantastic: https://www.amazon.com/dp/B07MMWH2YB
fennecfoxy
Lmao no, my doorbell is one (doesn't have a battery at) and has been going for 7 years strong, as long as I've lived in this place.
Sure you have to press it very slightly harder than a regular switch and the travel is a little more, but not by much.
I think the doorbell cost like £20 in 2020, actually lemme check Amazon...ah in fact it was 15.99£ (now it's £20.99 hmmm) "TECKNET self powered doorbell".
IshKebab
The Quinetic switches I use are extremely reliable and consistent. I've been mentally making a note of when the switch does not trigger the light, and it actually hasn't happened once yet and I've been using them for about 10 years.
You're right that they're expensive and need a decent activation force. They also are quite large and make a quite loud clicking noise which might be annoying for a sensor application.
Terr_
> for detecting other events like doors opening/closing etc.
If any of those doors are important for security, then I'd want something an intruder can't easily jam or spoof.
nh2
A big benefit of piezo-powered electronics is that they can do all the usual stuff, such storing state, or cryptography to prevent spoofing, which the ultrasonic approach from the article cannot do.
IshKebab
I use these kinetic switches all the time (the Quinetic brand is great and reliable; I've tried a Chinese one once and it died after a few months).
They're good but relatively expensive and relatively large. So I can kind of see why this might make sense. On the other hand having to put ultrasonic microphones all through your house is clearly much worse than a radio receiver, so I'd say these are a bit of a gimmick still.
anVlad11
It's research, not a product. Even with that, framing it as a smart home sensor in the press release is a stretch.
1) 93.75% success rate in controlled conditions, 92.1% in a somewhat-realistic deployment scenario - too low for reliability. I wouldn't use something like that to trigger smart home automations.
2) Range hardcapped at ~1m due to how ultrasound works, you can't centralize detection. Their answer is to give everyone in the household a wearable receiver, which is eeeeeeeh idk, doesn't look consumer-friendly to me.
3) Paper suggests a mix of durable and consumable parts for the transmitter. Their numbers show that the 3d-printed PLA cantilever needs to be replaced every 900 cycles or so. Should work fine, but...
4) ...every transmitter pair needs to be tuned per-setup, every time. Not a plug&play in the consumer sense.
svnt
This is the big constraint:
> 2) Range hardcapped at ~1m due to how ultrasound works, you can't centralize detection. Their answer is to give everyone in the household a wearable receiver, which is eeeeeeeh idk, doesn't look consumer-friendly to me.
Sure yes if you could do this with an always-listening smartphone or smartwatch that would be workable, but even then it constrains it to an occupant-activity detector.
Fixing that would require in the best case prompting an app install when visitors arrive. And still it is deaf to any other changes such as a door closing in the wind.
All possible, but feels several technosocial cycles away. Interesting to think about anyway.
nine_k
Could be more interesting for hard-to-reach underwater sensors. Water attenuates RF quite severely, but is good at conducting ultrasound. The response would have to be in ultrasound, too, of course.
cucumber3732842
From the artwork it looks like they're targeting industrial use. Seems like a low grade replacement for bar/qr code scanning. The "wearable" (more likely integrated into some other thing than worn IMO) receiver seems to point in that direction too.
Author probably has a specific use case in mind. Probably some application where EM emissions are undesirable or power is complicated that has thus far resisted automated industrial data entry. Investigating the use of something like ultrasound would align with constraints like that. Someone (department head? PR department?) said that was too niche and to make up some bullshit with mass market appeal.
abirch
5) These can be great if you want them to be monitored, but if I'm using my wife's toilet when I'm not supposed to, I'll simply hold the disk when I lift the seat.
Zigurd
My father was an engineer at Zenith when they were developing the Space Command TV remote control. This was a couple years before I was born, so by the time I got interested in hacking, Zenith TVs with this remote were commonplace. When visiting my friends homes I would prank them by jangling my keys and making the TV louder or quieter and randomly change channels. This presents new opportunities.
mmooss
Wow, I never heard of these. They operated on sound. Here's an article with photos, including some internals and the history of its engineering:
https://www.theverge.com/23810061/zenith-space-command-remot...
I wonder how reliable they were?
MrEricSir
Not very reliable. The remote only had four buttons (volume up/down, channel up/down) and various sounds like kitchen appliances, flushing toilets, and jingling keys would be interpreted as remote control actions by the TV.
My grandfather had one; he seemed to find it more entertaining to talk to people about it than to actual use it.
jacquesm
Blaupunkt (in the early 80s) had a similar system which was a lot more reliable also based on ultrasound, they used an encoding that was a bit less likely to show up in normal environmental sounds.
mmooss
Doesn't / didn't Blaupunkt make hi-fidelity audio equipment? I would think the range of sounds output by its speakers would make finding distinct sounds difficult. Maybe their audio expertise came in handy.
jacquesm
Yes, they did, but this was on a TV set, a - for the time - large color TV. It was a pretty weird little box, I have been searching but can't find an image for it.
inventor7777
This is a neat idea.
Personally, I would not find it useful as they seem relatively fragile and if the receiver is not bulletproof and VERY sensitive then it could miss state changes.
However, it would be interesting to see how it would work if you were able to have different ones on different frequencies with one main receiver. That would make a cost effective way to track cabinets, doors, etc in the same room.
ElijahLynn
What a brilliant concept, useful for so many applications!
The linked Instagram video was really useful and understanding the applications. I highly recommend watching that too. In addition to reading the article.
superxpro12
This is a very clever idea. However i think almost all smartphone microphone recorders cap out at 44.1khz or 48khz sample rate. Some have 96khz, but im not sure what is compatible with modern devices. That's going to limit how much frequency spectrum these fingerprints have to work with.
PunchyHamster
We've come full circle; one of first TV remotes used tuned pipes to generate sound driving the circuitry
jacquesm
So, in the true spirit of the HN dismissive comment, but this time I think it really does have its place.
Ultrasonic is DOA, sorry, but that just won't do. It's already a nuisance to have all these switching supplies that mess up your hearing (and some can be surprisingly loud), using it for power delivery is really a non-starter.
There was a company that planned on using ultrasonic for power delivery to smart phones, every engineer with some ultrasonic experience said it wasn't going to work and they just kept going until they - predictably - went out of business.
https://en.wikipedia.org/wiki/SonicEnergy (formerly Ubeam).
Just wishing it exists does not mean it is possible or practical, that's right up there with Theranos (and I think Theranos actually had a better chance of working even though that chance was extremely slim).
There are interesting start-ups around the theme of energy scavenging though, that's a far more realistic but still extremely challenging proposition.
robotresearcher
You may have misunderstood. Ultrasound is not being used here to deliver power to these 'sensors'. The devices give off distinctive ultrasound noises when they are bashed by things, like little cymbals. They are not really sensors - they transduce a mechanical input to a high-frequency mechanical output. To be used as a sensor you need a microphone and (typically) an AtoD as well.
Since it's just a little signal, there's very little power in it, so while your pet might hear it, and maybe it'll cause your noise-canceling headphone to squawk, it's not going to have enough energy to hurt anything.
JK-Swizzle
Did you read the article? It was not about ultrasonic power delivery. I’d describe it more as tuned ultrasonic bells.
jacquesm
Ahh I completely misunderstood the directional flow, thank you for the correction.
kumarvvr
Would these maintain their signature under repeated use? Or regular wear and tear?
deckar01
I have a suspicion the room reverb of anything other than that guy’s lab is enough to break it.
pshirshov
Same for EnOcean (energy harvesting ones). But most of them are too expensive for wide adoption (€50 for a temperature+humidity sensor is bit too much).
itissid
Wonderful. ultrasonic range emission having high S/N is amazing too. My hero usecase for this is to use these for behavioral therapy: Have a ring or a bracelet, thus without reaching for a phone or a notepad, record when a negative thought happens, i.e. a counter, or generate a sequence of ultrasonic sounds to map to specific kinds of thoughts. Have a sensor record and log them. I would then analyze the data across multiple days. My current method is recording them in obsidian.
rustyhancock
If you're old enough you might remember the Zenith Space Commander (I'm not old enough to have seen one in use).
It was an early TV remote that used spring loaded strikers controlled by buttons on the remote. The strikers hit tuned metal bars that rang out at ultrasonic frequencies the TV detected.
A links below but honestly it's the kind of topic that seems to never be covered well by a single resource. There are YouTube videos showing the inside of the controller and the striker.
[0] https://forums.atari.io/topic/10559-zenith-space-command-vin...
NoSalt
> "and cost only a few cents each"
Now companies are desperately trying to figure out how to jack up the price to $10.00 each without us knowing they are ripping us off.
tomaskafka
Finally, we are making the smart surveillance dust from the famous "Don't Make Smart Surveillance Dust" novel!
Eduard
range of barely 3 meters, doesn't mesh, purely unidirectional, only applicable as a sensor for collision detection, still needs a powered microphone on the receiving side, most likely wears out.
This isn't a smart home sensor.
chakintosh
> ... and counting reps in the gym
People need smart devices to count their reps !?
retired
No, but it’s nice if the reps are automatically fed into my spreadsheet for keeping track of progress.
tencentshill
What about durability? They are mechanical metal pieces, so would eventually wear down or change tone.
combocosmo
It's a unique idea that I could see being useful in select situations. The reliance on wearable microphones sounds like a downside.
Also I guess this might be annoying for pets that can hear well beyond 20 kHz.
tetris11
Im not sure I got it. It generates acoustic signals and a microphone server picks them up.
If so, will it penetrate through walls?
lesuorac
Well, idk if these do but you can certainly make passive devices that penetrate walls.
See http://en.wikipedia.org/wiki/The_Thing_(listening_device)
jacquesm
Radio waves != sound waves.
croes
Unlikely because it’s ultrasonic sound, at least if you have brick walls.
Could work for drywalls
jacquesm
Not a chance. Drywall will absorb this like a sponge. These frequencies are really high and will reflect off hard or thin surfaces, drywall is relatively soft, more often than not has insulation packed into the center and is usually covered in some kind of stucco or grout. Zero chance of penetration.
Just stand on the other side of a drywall and see how well high pitched normally audible sounds get through vs the much lower frequency sounds. It sounds decidedly muffled because all the high has been absorbed.
fragmede
The microphone is on a smart watch the user is wearing.
alberto467
Can i not trigger the automations from my smart watch then?
ga_to
Sure could, but then you would need to do the thing AND think about doing the triggering and then find the trigger button on your watch. This way you wouldn't have to think about it, because it's automated. Triggering something manually also doesn't really count as 'automation' I would say.
croes
Do you need a signal that tells you the window is open if you are in the same room?
SimplyUnknown
Obviously not, but there is larger potential than that. A microphone in a watch or phone can pick up the signal and relay the trigger to another server via for example MQTT. Then, you can have homeassistant act upon this signal.
The flow is then Open door --> Signal triggers --> Signal caught by microphone --> Microphone device relays to server --> Server turns on smart lighting in that room.
There is a lot more that you can do, but this is just an example. The microphone to pick it up is a limitations, but the gain is:
- reduced power usage as the signal generators are not power-operated
- less waste as no empty batteries need to be discarded (if non-rechargeable batteries are used)
- improved security because the signal generators are not connected to the internet, reducing the attack surface.
hilti
If you are constantly looking at your smartphone and ignore the real world ... yes ;-)
fragmede
Now imagine you're living with 10 people at a facility/station/factory/depot, and there are 5 windows across a dozen externally facing rooms.
cyberax
Trivia time! The first practical wireless remote control for TVs also used ultrasound: https://www.youtube.com/watch?v=MLPk1Us62xQ
buescher
Right, and they were superseded by battery-powered infrared remotes for good reasons. I would recommend revisiting those reasons before proposing this sort of technology for wireless sensors.
jacquesm
And that's just signalling, not power delivery.
alnwlsn
Mostly it was that electronics got cheap enough that you didn't need to keep building the bulky and expensive mechanical version. The first wireless remotes that used batteries were still ultrasonic, they just generated the tone electronically instead of by striking a metal bar. Plus, you could have way more buttons with an electric version; you would need a bar per function for the mechanical way.
dzhiurgis
Bought my house almost 3 years ago and put bunch of battery operated sensors, lights, switches. None of them died yet. None of the problems were due to batteries.
Most common one - kiddo smashes it 5 times which kicks it into pairing mode...
therealfigtree
Titlegore
mschuster91
Interesting idea and reminds me of the German train security system PZB which acts completely electricity-free at the signal - a mechanical switch connects a capacitor to de-tune a magnetic resonance circuit, which is then detected by a passing train's magloop transmitter.
Unfortunately... I see issues:
> Those frequencies are above 20 kilohertz, which is the upper limit of sounds humans can hear.
Yeah. Humans' range ends there, at least in adulthood. But what about pets? Wildlife? Children and toddlers? Or just people that take care of their hearing by not frying their ears with too much exposure to loudness? It's already an issue with "mosquito teenager repellant" devices.
tamimio
Get an SDR, tune into the frequency, and troll the home automation system! Given that it’s not of a high frequency, the attack can be done from a distance with proper antenna, and the frequencies use a hardcoded algorithm. Hell, I wouldn’t be surprised to see flipper zero addon to that (hardware through GPIO and software) for portability.
Eduard
SDR can't ultrasound
tamimio
Yes it does, my LimeSDR can go to 100khz. If you need less, just get a piezoelectric transducer paired with signal generator like arduino or esp32, might add drive circuit/gate driver to improve it. It’s very doable, and you can programmatically troll the system knowing the algo, and I am saying “troll” but obviously you can have serious use of that.
mystraline
Where the profit in acoustic tuned sensors?
Sensors must be using batteries, wear out in a month or so, tied to an oppressive cloud seevice, and regular up-sells of things that would be standard but we stratified types of paying users.
For a dotedu, this is perfectly fine. But this wouldn't pass muster as a real product. You can't do all the HorribleUsesAsAService like almost all IoT hardware is.
ogig
I can see some uses, but calling this system batteries free seems a stretch. A sensor is worth nothing if it can't be read, and to read this you need a powered microphone and computing. Some already common magnetic door systems do the same; door plate and magnet movement is enough to create a detectable current, (using no external power), then that signal is read and computed by an electronic/digital system (using power).
SOLAR_FIELDS
Even the layout you describe has massive advantages over the status quo from a placement perspective. Having a reduced footprint device that goes in the actual measurement location that can phone home to a more robust central location like this is not only already very common but also the existing solutions that do it still suffer from the design constraint of requiring a battery which this innovation goes a long way towards
phh
I'm on the side of "clever, fun, but feels useless". But to defend the project, all sensors require a powered central system. It's pretty common for Zigbee to have one repeater per room [1], which is just what is needed for this system.
[1] Because any AC-powered Zigbee device is a repeater, so just a bulb or a plug is enough
For a brief, beautiful moment from the headline I thought "oh good, more PoE sensors finally happening!" doho. But no not just about battery but any power at all, and an interesting approach for further research. Of course to actually get data from still requires powered devices but in a lot of cases it'd be much easier to have that be a single or small number of more easily placed central units vs every single sensor tag separately. Ultra low cost and simplicity are values all their own in terms of applications.
My biggest immediately question though and one I'm a little surprised not see addressed, even at the research stage, is any mention of other animals. There is a bunch there about the ultrasonic frequency being well above the human limit of ~20 kHz. But IIRC for example dogs can hear up to like 45-60 kHz, and cats all the way to 65-85 kHz. I assume lots and lots of other animals also can perceive sounds well beyond human senses. Noise pollution is already a somewhat unrecognized but big problem for all sorts of life around us (not that it's irrelevant to human health either), so if more use of ultrasonics made that worse that's a concern. And as a practical matter the product market is probably going to shrink pretty dramatically if it drives pets mad, a lot of people have pets nowadays they care about a great deal. For that matter even in public environments if it messed with service dogs that might have ADA or equivalent implications.
Still, good reminder of various side channels one doesn't always think about.