Mines a real "pet" project. I installed a bluetooth signal/sensor in my dogs harness, put an infrared sensor strip on backdoor and hacked together something like twillo for notifications. When I let him outside, I know when he is back at the door because his motion gets picked up by the sensor and a text message gets fired off to say "Woof. Let me in. Love Simon." This didn't take me long to build and it gets the job done. Still refining. It's all good fun... COST: under $19 for all electronics.
Do you have a blog describing the parts and where you got them? I'm interested in doing the same type of thing, but for a different situation and was going about it differently.
