The dead man's trigger was a heart rate monitor and radio transmitter worn by Martin Keamy.
Omar strapped the dead man's trigger to Keamy's left arm inside the armory of the freighter Kahana. The device consisted of a strap worn around the waist with a raised section in the middle and a smaller rectangular unit with a two-color light—green for alive and red for dead.
When Captain Gault confronted Keamy at gunpoint as Keamy attempted to return to the Island, Keamy showed Gault the device and said it would not be a good idea to shoot him. When Gault was distracted, Keamy shot him.
Keamy later revealed to Benjamin Linus in the Orchid that the dead man's trigger monitored his heart rate. If his heart were to stop, then the device would send a radio signal back to a receiver on the freighter which would cause 500 lbs. of C-4 to detonate, sinking the ship. Keamy referred to the device as "a life insurance policy" and a "dead man's trigger".
After Ben fatally wounded Keamy, the device triggered the C-4 bomb, destroying the Kahana despite Michael's best efforts.
- This device is responsible for the deaths of at least six people (Hendricks, Jeff, three redshirts, Michael, and questionably Jin.)