The Detonator is a Rare Remote Trigger in Unturned 3. It is used in conjunction with a Charge.
Right clicking (by default) with the Detonator is used to activate the Charge you are looking at and left clicking (by default) will detonate them. You are not restricted to a single active Charge, and may have up to eight active. With more than one active, they will detonate in the order that they were activated.
The highlight around a Charge signifies its current state. Red means it is disabled, yellow means it is selected while disabled, green means it is active, and blue means it is selected while active.