Pretty interning idea. From their website...
Disc Beeper is an electronic device that is centrally placed underneath a Disc or Frisbee that allows players to easily find their Disc or Frisbee especially during the sport "Disc Golf."
http://www.youtube.com/watch?v=8gS3AUhoBOI&feature=player_embedded
This device only weighs 6 grams and shows absolutely no noticeable effect on disc flight.
Disc Beeper also has a waterproof design. It has 3 distinct modes that allows up to 3 players to play at once. Disc Beeper has a push-button to turn it on requiring 550 grams of force to engage. Once the Disc Beeper is turned on, there is a 45 second delay to allow launch and attempted retrieval, allowing the user to throw it and will beep every 3 seconds until you turn it off.
Disc Beeper is rechargeable via included micro usb cord. It holds up to 7-8 hours under 1 charge of 1 hour.
http://discbeeper.com/index.html
This post is for information only. Product not available in stores or proshop.
(thanks to Ian Funston for the lead)