The dead man's trigger was a heart rate monitor and radio transmitter worn by Martin Keamy. It acted as a fail-deadly device that would trigger the destruction of the Kahana in the event of Keamy's death.
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 represented the heart beating and red represented the heart stopping.
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. ("Cabin Fever")
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".
- This device is responsible for the deaths of everyone who was on board of the Kahana except Jin.
- This device would have not been able to transmit the signal to the freighter as far down under the ground it was in the Orchid. Cell phones don't even get good reception when under concrete structure. Ben said that the elevator goes "deep". One explanation could be that the device doesn't trigger the explosion at loss of signal, but only when the explosive receives a "dead" signal from the transmitter (although this theory only proves valid if the device had been transported above-ground after Keamy was killed).
- The prop used to create this device is very similar to a Korg digital guitar tuner.