Ideally we would measure and store the location, speed and acceleration of a vehicle, say, once per second (or even faster), in order to map out the full speed 'profile' of a vehicle in detail.
However, in many scenarios or countries with weaker communications infrastructure this volume of data is not necessary or possible to send, either over cellular or satellite networks. Some classes of sensor, such as accelerometer, sample at even faster rates at up to 10-100 Hz (ten to 100 times per second) in order to measure 'spikes' or sudden changes in acceleration.
This motivates the introduction of 'exception alerts' which are recorded only when the speed or acceleration exceeds some value for more than a certain amount of time. Although threshold-based exceptions don’t tell the whole story about the driving style, they aim to capture information about undesirable driver behaviour in the same way that a speed camera would act on vehicles travelling faster than a certain speed.
Both acceleration and speed thresholds can be customised, and usually take into account a variety of factors such as the country (regulations, speed limits) and the vehicle type (light vehicle versus heavy vehicle).