[XCSSA] OT: simple, reliable wireless sensors

[xcssa@xcssa.org]

Hey folks,

Supposing that I could not run wire to all the NC sensors I want to
deploy without drilling holes and running cable, what would be a
relatively inexpensive wireless communication protocol that only needs
to transmit a short-range binary signal (open/closed), without
interfering with extant 802.11 and 5.2GHz ranges?  I have a ham
license but don't want to use the spectrum as a trash bin.

I want to avoid having to buy a PC and a wifi NIC, and run off
batteries for, say, 24 hours,
so it need to be relatively simple I would think.

I was thinking of a timer circuit and a DTMF encoder that sends a
"circuit closed" heartbeat every N seconds, and maybe a "circuit open"
code for immediate notification.

Also, I'd like a small, cheap design for another module where the only
requirements are that it be battery-powered and listen for a (very
rare) signal and then activate another circuit.  It would need to
consume virtually no power unless the signal is sent.

I'm not too worried about jamming or stealth, I just want something reliable.

If anyone has any info on Tesla-style radio-powered circuits, I
suppose like RFID, I'd be interested in those too.

Let the brainstorming begin!
-- 
"The obvious mathematical breakthrough would be the development of an
easy way to factor large prime numbers.'' [sic] -- Bill Gates  -><-
<URL:http://www.subspacefield.org/~travis/>
GPG fingerprint: 9D3F 395A DAC5 5CCC 9066  151D 0A6B 4098 0C55 1484