and like you say, it's channel!
Discussion
Hmm. I'll keep this in mind. Not reinventing the wheel is nice. But you hit the next problem - battery. Need those nifty diamond batteries
yeah that's why i mentioned bluetooth because it uses much less power
but let's say you pick a "rugged" phone like a Blackview, which has a massive battery, they are a bit big and chunky but they run recent versions of android and are decently configurable, the lifespan is gonna be pretty good alone
then there is also the possibility of having the device plug into a beefy battery bank, assuming you can find a device that will actually go into sleep mode with the power plugged in, should be able to
if you unlock developer mode, also, probably you can tweak some more things in the wireless network and sleep mode controls to even further reduce its idle power draw
if it's doing nothing but listening to the wifi, and it's got a 4000+mAh battery like a typical rugged phone, with all the dev mode tweaks on, i bet it would run for maybe 2-4 weeks between charges, possibly longer, kinda depends on how leaky the battery is, some batteries stay charged longer than others
Now I'm imagining things that last years. Like, no draw on battery at all, until a tiny charge makes it through an electrical lock on the antenna. If that makes sense. This might be mission creep.
well, probably some kind of NFC device can be used like this... it would need get enough power to actuate a hard switch, like, think of a very small solenoid attached to an antenna that you just need to send a signal at that frequency, then the hard switch closes and connects the device to the battery and it automatically powers up
years, i suppose a brand new fully charged lithium ion battery is gonna probably have enoughu charge to be useful for at least a year, maybe two, without anything connected to it... a lead acid battery has probably got a lower leak rate but much bigger
i don't know exactly how long the batteries hold charge without anything connected, but all the devices i've bought in the last few years have come charged and i believe they charge them 100% and typically they were around 60-80% on first power up, so i'd guess that's losing about 20% per 6 months, so yeah, a couple of years is feasible, if you can make an induction trigger to switch the power on
also, if you can make something a bit bigger, all this is easy to do with a raspberry pi and a few extra pieces, a fat battery
another thing too is if you can hide it within a relatively small range, like half a foot under ground, there are fully battery-free passive bluetooth tags and similar, NFC, that will respond within a short distance, but be hard to locate without knowing they are there, even with a metal detector