We developed an Ultimate Security Device (USD) that can, in case of intrusion or external attack, blow up a safetycritical component such as memory device. The device consists of two active parts (1) a pyroMEMS ignites in a fraction of millisecond (2) a mass of reactive composite, both encapsulated into a printed hermetic cap and placed over the sensitive component to be protected. After the presentation of the design and integration of the USD, we demonstrated that 400 mg of reactive composite permits to irreversibly destroy the silicon chips (~118 mm 3) in less than 10 ms. This ultimate security device provides a speedy and automatic response and can be programmed for tunable actions (generation of pressure burst, heat, chemical species) to implement relevant emergency safety responses.