Excalibur utilizes two electro-mechanical kinetic switches to detect firing and impact. The first one powers up the electronics. The second begins the explosive train (detonation). Both are installed into their respective subsystems at L-3, and then get delivered to Raytheon for final assembly and testing. I designed both devices, and our company (CIRCOR Aerospace, Aerodyne Controls division) manufactures them.
Virtually all major and many minor weapons systems use my hardware, including Hellfire, Hellfire II Romeo, Sea Sparrow, JDAM, JASM, TOW II, Mk48 ADCAP, FMU-139, FMU-142, FMU-152, Small Diameter Bomb, SMAW II, M72 ASM FFE, SM2, SM3, and many others.