Airbag sensors are actually small electronic pieces that sense when an accident has taken place. They are designed to respond to circumstances such as increased pressure resulting from a collision and sudden stopping.
Airbag sensors can be used to detect how many people are in the vehicle and measure wheel speed, impact and brake pressure. The airbag control unit is usually built into the front section of the cabin. The unit is programmed to study the information that it receives in order to activate seat belt locks, airbag deployment, automatic door locks and other safety measures.
The two different types of airbag sensors are mechanical and electrical. Some electrical sensors use electromechanical "bauble and ball" mechanisms designed to release a ball from a magnet, which rolls into a tube before hitting a switch and completing an electrical connection. Mechanical sensors are designed to work independently from their electrical counterparts, and they utilize a firing pin to activate a compact explosion after an accident occurs.
One difference between the two different types of systems is that mechanical sensors can't be shut off after the battery has been disconnected the same way that electrical ones can, since mechanical sensors don't require a power source.