From Lexicanum

The Failsafe Detonator is a battlesuit mounted device, more commonly known as a self-destruct device. If a unit is in trouble of being overrun and the situation is sufficiently desperate, a character can active this device, causing his battlesuit to explode in a deadly blast, almost guaranteed to destroy everything around him. This will, of course, lead to the demise of the character but could save the rest of the squad. It is seen as the ultimate expression of the Greater Good.^1-p26

Sources

• ¹:Codex: Tau Empire (4th Edition)