another thing that might work is one of those personal alarms.  My aunt had one, and it send out one hell of a noise.  Just rig it in the fuse so the pin is fastened and the actual unit is just resting in the fuse.  I doubt any normal flying would set it off, but in a crash, it should work.  Only thing to worry about is the weight gain.  And always have your name and phone number/AMA or MAAC number.