I bought a half dozen lost plane "beepers" on EBAY.  They were about $8.00 each. They sound off after 60 seconds of inactivity. Of course, they assume that your battery will still be intact after the plane comes down.  The sound is OK for about 40 yards or so, which helps.  </p>

There are fancy ones that actually track a specific plane with a radio beacon. I haven't tried those.  Most of my concerns are when I put the plane down in a corn field and I need help locating it when I am closing in.  Rich </p>