Good day to all. I have a 4-year-old cat who discovered this past summer that he=20 *really* liked being outdoors. He was strictly an indoor cat up=20 until that time but now he gets cranky if he's not allowed outside. That wasn't a problem during the summer months - and not even that=20 much problem during the fall. He spent literally weeks outside and=20 the only time that I saw him was when I called him every evening to=20 come get supper (when it got dark). But now its winter outside and he is spending his days inside. We've=20 got a foot or more of snow and the temperature plummeted down to -30C=20 or so this past week. He won't be a happy camper if he has to stay=20 outside for extended periods. So, several weeks ago, I installed a cat door in my bedroom=20 window. It took him a while to figure out how to get outside but he=20 sure had no problem figuring out how to come back inside . Now=20 he comes and goes as he pleases. I knew that it would only be a matter of time before some of his=20 neighborhood feline friends also discovered this wonderful door into=20 warmth, fresh water, and food. It happened today. So now I've locked the cat door into allowing traffic from IN to OUT=20 only. I have to let the cat in manually when he wants in. That's OK=20 when I'm here but not good during the day when I'm at work. I want to put a small, short-range transmitter on his collar so that=20 I can have a pair of RC servos un-block the 'IN' traffic=20 direction. I thought about using permanent magnets on his collar,=20 but am unhappy with the prospect of them gathering ferrous debris as=20 well as the very short range operation. I think that RF is my best=20 bet. Modulated IR would be a close second choice. Is anyone aware of an inexpensive, short-range RF link that has a=20 transmitter that will operate for several months from a single=20 battery change? It really only needs a foot or so of range. I don't=20 really care how large the receiver is but the transmitter would=20 ideally be in a waterproof enclosure that is suitable for attaching=20 to collar for a small cat. I'd rather purchase a ready-made transmitter if possible (and=20 matching receiver). Is anyone aware of something that might be suitable? Many thanks! dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .