Distress signal unit

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A Distress Signal Unit, or D.S.U , is a piece of equipment used by firefighters while working in hazardous areas. Normally used in conjunction with breathing apparatus, it is a small, battery powered item attached to the breathing apparatus harness and enables the firefighter to summon help by means of activating a loud, piercing electronic bleeper.

Early models were only able to be activated manually, however in recent years the equipment has incorporated movement sensors. This means that if the firefighter remains stationary for more than 30 seconds, the unit will activate automatically. The unit is equipped with a key which when removed arms the unit. This is left outside the hazard area with an entry control officer. When the unit activates it can only be switched off by inserting this key.