[037]

A little tangential, but are these things safe for humans? I have a couple of LD2410 devices and I’d like to use one of them with ESPHome in the bedroom. I did some research and they seem to be very low power and safe, but you know, before sleeping with a radar pointing at us all night long, I’m looking for as much feedback as possible.

[perlgeek]

Non-ionizing radio waves are generally safe for humans.

The only mechanism besides ionization that could harm humans is through the transfer of lots of power into the human body (think soldiers keeping themselves warm by stepping in front of a radar emitter).

So let's try to do a ballpark estimate of how much that could matter.

I haven't found (from a quick search) any data regarding the transmission power, but the data sheet at https://fcc.report/FCC-ID/2AD56HLK-LD2410B-P/6620025.pdf says the average current consumption is 79mA at 5V, which means it uses 0.4W.

How much of that is actually transmitted? I'd guess 10%-50% (likely much less, but let's go with this more conservative estimate, from a safety perspective), so now we're in the range of 40mW to 200mW.

If you absorb 1/4th of that (again, somewhat conservative estimate; you'll likely also reflect some, and most of it is going to pass you), we're at 10mW to 50mW extra power that is absorbed by your tissue.

Again, this is a super high (and thus for our purpose, conservative) estimate. Somebody else in this thread mentioned microwatts being absorbed, which sounds much more plausible.

To put this into context, the base level of power that an adult human operates on at rest is about 100W. This is a factor of 500 to 2500 more than the power absorbed from our millimeter wave radar. Unless all the absorption happens by a very specific and sensitive part of the body (like your eyes or so), this should just be background noise.

If you want another perspective, you could try to compare it with whatever radiation (both RF and heat) that your phone emits, that you likely carry in your pocket for hours at a time.

[wyager]

> The only mechanism besides ionization that could harm humans [is heat]

This claim is, IMO, too strong given available evidence.

There are many chemical interactions with characteristic energies well below 1eV, or any reasonable threshold for "ionizing". Photons can couple with these interactions without ionizing anything. 4GHz range is probably fine, because the per photon energy is a small fraction of a mEv, but even then I would not rule out the possibility of multiple photons coupling to a structure without the imparted energy immediately being dispersed as heat.

Any time you have EM with low entropy/etendue, it is always theoretically possible for interactions to occur outside of the thermal regime.

[lpcvoid]

>soldiers keeping themselves warm by stepping in front of a radar emitter

Holy, did people actually do this? A quick search yielded no results. Not sure if thankful or not.

[simondanerd]

Works, it's a weird feeling, speaking from experience. HF antennas can give some respectable burns too.

But the effects are debated and not entirely scientific: https://www.reddit.com/r/army/comments/13r6hod/i_keep_being_...

[moffkalast]

Weren't microwave ovens invented because someone's chocolate melted in their pocket while operating a radio transmitter? Maybe it's just a lady godiva story since it seems weird that the person wouldn't feel overly hot as well, but maybe.

[marcosdumay]

It's a well known story, he was doing maintenance:

https://en.wikipedia.org/wiki/Microwave_oven#Discovery

The thing is, you don't need a lot of extra heat to melt a chocolate bar on your pocket. It's perfectly possible that everybody felt hot when working on an active radar, but didn't discuss it or maybe even notice the correlation.

[InvisGhost]

The bit on that wikipedia page about reanimating frozen hamsters is a bit of a sci-fi nightmare

[moffkalast]

Tom Scott has a great video on that: https://www.youtube.com/watch?v=2tdiKTSdE9Y

[moffkalast]

Oh wow it's even known what brand of a bar it was, funny that.

> The first food deliberately cooked with Spencer's microwave oven was popcorn, and the second was an egg, which exploded in the face of one of the experimenters.

They were having a blast I see.

[05]

Some phones have a SAR of almost 2W/kg, compared to that milliwatts of 10GHz RF are nothing. Not to mention that with standard energy dissipation formula of E~R^(-2) you're getting into microwatts at any practical distance from the antenna.

[t0mas88]

I have these all around the house, but not in the bedrooms. I use weight sensors to detect that someone is in bed and traditional PIR for motion in bedrooms.

Probably overly careful, but I didn't want to point a radar at my sleeping kids (and myself) for 12 hours per day. Similar for the WiFi access point upstairs, it's only in the hallway and not at maximum power.

[Avamander]

> Probably overly careful, but I didn't want to point a radar at my sleeping kids (and myself) for 12 hours per day.

While I understand the sentiment. It's very very unlikely to be dangerous and there are plenty of other environmental dangers.

The biggest being the sun. But the most common man-made ones are probably auditory. Like toys and TVs being too loud or high-frequency sounds blasted from speakers in malls or under bridges to avoid "loitering."

[moffkalast]

Yeah on one hand you have people afraid of wifi and simultaneously sending their kids to play all day outside in UV index 11 without a hat or sunscreen. Things that are "natural" being inherently safe and anything technological literally death itself.

[davidwritesbugs]

Loud toys are definitely dangerous for my children, they make me angry.

[037]

I agree with you, especially regarding children and anyone who hasn’t explicitly made this choice, which is why I asked the question. The only thing is, I suspect we get scared by certain words, like “radar” and “microwaves”, and then we might spend all day with our heads next to a Wi-Fi router or a phone constantly downloading files on 4G.

For example: maybe the ESP32 transmitting the bed weight exposes us to more danger than the radar sensor (that can also be placed very far from the bed)? Maybe with our smartphones charging on the nightstand too.

I’m not a big fan of fear-based, illogical decisions. But, again, I understand perfectly.

[rpaddock]

The site Microwave News keeps up on the latest health aspects of such things.

https://www.microwavenews.com