Which one of the following is not an essential component of Improvised Explosive Device (IED) ?

An Improvised Explosive Device (IED) is typically defined by four primary components, often summarized by the acronym PIES: Power source, Initiator, Explosive, and Switch. The Explosive is the main charge that creates the blast, the Detonator (Initiator) is the small quantity of sensitive explosive that triggers the main charge, and the Power source (usually a battery) provides the electrical energy to the initiator. While a Switch (trigger) is an essential component, a Mechanical timer/Mechanical clock is only one specific variety of switch. IEDs can be triggered by many other means, such as remote control, pressure plates, or tripwires, meaning a mechanical timer is not a universal or essential requirement for the device to function.