Love this comment. Not a hardware guy but it seems to me it would be really cool to "deconstruct" bluetooth to the point where you just have a d-to-a converter

Love this comment. Not a hardware guy but it seems to me it would be really cool to "deconstruct" bluetooth to the point where you just have a d-to-a converter periodically pump a small mutable memory region onto a tiny antenna ("shout into the void"). That memory region is written to periodically by the sensors, which are themselves tiny MEMS units that only sense and write to memory when powered; you periodically send power to them. Encryption would happen either before write or just before transmission. To keep things really simple, you could hardcode a secret into each device, only accessible by the end-user by opening the device and looking, maybe with a microscope for extra security. Alternatively, you might set it up to repetatively broadcast the secret on first power up and then have a one-time switch that the user "crushes" to it into sensing mode. (and if you hit that switch without the secret, or lose the secret, you now have a brick). I'm not sure how compatible this would be with bluetooth protocol, which I know is enormous, and is highly stateful (pairing, etc). One can hope.