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Old-school SRS used bumper- or radiator-mounted "crash sensors." Current-generation systems use digital accelerometers that are often integrated into the airbag control monitor.
Some advanced airbag inflators are multi-stage or variable output, so you need a sensor that provides a data stream rather than a single-use one-and-done crash sensor.
There are a minimum of three sensors in the car(third gen SRS). Almost surely there is a sensor in the airbag triggering and control unit. There is a multi-axis, multi-trigger unit on each side of the car, often near the base/midpoint of the B pillar(our cars would be just behind the door latch). For an airbag to deploy there must be a quorum of sensor activations to deploy the airbag.
Not something to mess with if you aren't skilled at airbag systems. I haven't worked on them since the first gen, and I won't touch one of the later units. Older unit front mounted sensors were at the base of the A pillar for Porsche, MB, Opel, Renault, Lotus, and a few others.