In most cases, all of my crashes have seperated the battery from the rest of the system so an alarm using the flight battery would be of little or no use. If you get a locator which has its own power supply (usually a 9 volt battery) you solve this problem but lose the advantages described above about being warned when you accidently leave the receiver on and the transmitter off. Also, the self powered unit must have its own switch which you must remember to turn on at the start of a flight. It will alarm you to turn that switch off when you land and turn off your transmitter though. These are just considerations you need to think about when you buy a locator.