DIY active cat collar GPS unit?

[casper.bang]

Your problem will be the weight/transmission distance ratio, you don't get anything for nothing. And the cat a stiff neck.

Right, which is why I'm focusing on a manual locating approach (go look for the cat) rather than automatic tracking (sit at home looking at a screen). I can live without always knowing where the cat goes, but I would love to have a tool to help look for the cat when/if it does not get home at night. From those requirements, there should be no weight/transmission issue - currently looking for a way to emit beacon pulses onto the 457KHz band (official avalanche victim transponder frequency*) and I reckon a 8mW 200ms pulse at 1Hz would run a while on a  3.7V 100mAh (370mWh) LiPo weighing just 2-3g.

PS: I live in Denmark where the highest "mountain" is 150m and the most amount of snow is 20-30cm so I am extremely unlikely to interfere with real avalanche distress scenarios.

[Sigmoid]

If I ever get the urge to build an evil genius stronghold, I'll have a herd of cats with videocameras for surveillance.

whats even better is to put a go pro camera on cat.

i dont think its very ethical, I would not do it to my cat.. but it is what it is

[Maxlor]

It occurred to me that the devices used for wildlife tracking might work. I found this store: http://wildlifematerials.com/store/index.php?s=m

They have trackers that can be affixed to mice or small birds and run several weeks, so finding something small for your cat shouldn't be a problem. And if you want to build instead of buy, maybe you can get some ideas from them.

[pickle9000]

I don't suppose a 3w cree and a remote to turn it on. You'd spot the cat but it would scare the crap out of it.