I've got a bunch of wireless alarm sensors left over from low cost DIY alarms that had to be replaced. You might know the sort of Chinese made alarms that you get on eBay. A lot of them operate on the same frequency, but I have no idea how they actually communicate over that frequency or if there's any kind of inter-manufacturer standard that they follow. Is there any chance a wireless sensor or remote could be paired with an alarm unit from another manufacturer? If not I'll probably chuck them all, though it would be a shame as some of the sensors, like the wireless smoke detector wasn't all that cheap.