check these
- RF Link Transmitter - 434MHz - WRL-10534 - SparkFun Electronics -
- RF Link Receiver - 4800bps (434MHz) - WRL-10532 - SparkFun Electronics -
low baud rate (4800) but as it only needs to send an node ID + detector ID (2 bytes) when something is detected that is not a problem. 500 feet optimal => 100 feet (30 mtrs) should be feasible.
Idea: the nodes should also warn for low battery.
Idea: an LDR could detect people approaching with a flash lights