The just-announced Garmin Chirp is a small (slightly larger than a quarter) capsule that serves as a combination beacon and communication device at the site of a geocache. The Chirp sells for $20 - $23, and weighs less than one ounce. The Chirp "stores hints, multicache coordinates, counts visitors and confirms the cache is nearby," states Garmin. It is waterproof and durable, and its battery is said to last about a year.
For the person who creates or monitors a geocache, Chirp benefits include the ability to transmit hints and tips, wirelessly provide instructions and coordinates for a multicache hide, and automated tracking and uploading of cache visitor counts.
For those seeking a cache that has a Chirp, benefits include notification of proximity to a cache (10-yard range), hints and tips provided by the cache creator, and automatic upload of coordinates of the next cache in a mutlicache hide.
The Chirp should not be buried, placed in a metal box, or hidden underwater, Garmin states, because its signal would be blocked. Also, I think that a Chirp should not be hidden in the geocache box itself, where it could potentially be stolen. Someone placing a Chirp could easily hide it in a nook near, but not in the cache and it would still serve its intended purpose without risk of theft.
On the downside, the Chirp is compatible only with select Garmin handheld GPS devices using ANT+ wireless technology, including certain Dakota, GPSMAP, and Oregon series models. Image © Garmin