An arrangement is provided for triggering a vehicle safety device. A proximity sensor (1) provides an output related to a distance to an object and/or the relative speed between the object and the sensor. A main accelerometer (2) is sensitive to acceleration in a predetermined direction. A supplementary accelerometer (3) is also provided. A first processing arrangement (4) performs an algorithm with the main algorithm, and is connected to receive an input from the proximity sensor and from the main accelerometer and to provide an output to a triggering signal generator (5). There is a second processing arrangement (7) which receives a signal from the main accelerometer (2) and also from the supplementary accelerometer (3). The second processing arrangement also provides an output connected to the said signal generator (5) to generate the triggering signal.