Very simple proximity activated switch (several inches range)?

Hello Instructables! I am looking for a simple electronic switch that will instantly turn on when it comes within a few inches (5-8) of a little beacon or antenna of some sort.

I would like to be able to have the beacon be small, and preferably flat in form factor, with the receiver/switch system being no larger than an inch square. For size constraints, watch batteries would be the most preferred power source. 

Would RFID be a good option for this? 

Preferably I don't want this to have to be hooked to a phone, and it would need to be something that I could conceivably make a PCB foror use a very small existing board like a TEENSY. 

iceng1 month ago
everything_that_moves_alarm.gif

Yeah, RFID is a good choice here. Sparkfun et al sell suitable modules.

ilpug (author)  steveastrouk1 month ago

That's what I was leaning towards but upon further research I have learned that RFID needs the antenna and coil to be held close to a certain orientation near each other to read. My application would have the receiver in a wrist wearable and the beacon on something else, and they would not always be oriented correctly in use. Are there omni-directionally reading RFID systems that would still fit the form factors?

Much depends on the antenna, and the sensitivity of the system, you can get results at extreme misorientations, if your receiver is sensitive enough.