An electric circuit module has a case made of a non-magnetic material. The case has an attachment portion for fixed mounting on a vehicle part made of a magnetic material and a permanent magnet fixed within the case. The module further has a Hall effect sensor fixed within the case in positional relation to the permanent magnet and the attachment portion such that the Hall effect sensor generates a first signal when the attachment portion of the case is fixedly attached to the vehicle part and a second signal different from the first signal when the attachment portion of the case is not so mounted. The module also has an electric circuit in the case with circuit elements responsive to the Hall effect sensor to provide a first mode of operation in response to the first signal and a second mode of operation in response to the second signal. The module is particularly useful when at least one of the electric circuit elements is an accelerometer, for example in a vehicle passive restraint deployment system. In such an application, the Hall effect sensor output indicates the validity of the accelerometer output signal as an indication of accelerations of the vehicle part and can thus help control the use of the accelerometer signal in determining restraint deployment.