Micro-Machined Sensor Needs No Power

The MEM-1A magnetically-actuated reed sensor requires no power for operation and is designed for switching CMOS gates and other low-power devices. The sensors measure 2.8 mm x 2 mm and are available with magnetic sensitivity ranges from 1.6 mT to 4.07 mT and are said to be tested to withstand up to 15 kg of shock from any direction.
These SPST sensors have a switching voltage of 3 Vdc maximum with a 10⁹ insulation resistance across the contact. They are available in tape-and-reel packaging, suitable for auto-placement equipment, and priced according to quantity.