Mass Movement Sensor Module (MMS)
There are two Mass movement sensor modules (MMS) in the C70. One is located under the cup holder in the center console and the other under the central rear seat.
The mass movement sensor module (MMS) is used to detect movement in the passenger compartment when the alarm is activated. The aim is to detect if somebody attempts to reach inside the vehicle to steal bag or similar.
When the alarm is activated, the central electronic module (CEM) checks the sensors.
The sensors communicate serially with the central electronic module (CEM). If two sensors are installed they are connected in parallel to the central electronic module (CEM).
The sensor that triggered the alarm can be detected by the Central electronic module (CEM) by differences in the data messages that are received from each Mass movement sensor module (MMS).
When the sensors are activated they transmit microwaves into the vehicle. The microwaves bounce back from the interior of the vehicle and the sensors react to changes in these reflected waves.
The Mass movement sensor module (MMS) functions a slightly different way in the C70. The sensors work as well with the roof open or closed.
If the roof is open, there is no surface that the microwaves can directly bounce off. However, the waves spread in the air and eventually bounce back to the object that is further away, for example, the roof of a car park or a tree that the vehicle is parked under.
To reduce he risk of a false alarm in this mode, the sensor measures the time from when it sent a pulse until it receives the same pulse back. If the reflection time is too long, i. e. the pulse has bounced on something further away than 1.5 meters, (4.92 feet) upwards from the sensor, the sensor will refer to the pulse changes.
On the other hand, if the time is within specified values, the pulse changes are interpreted as a movement in the vehicle and the alarm will be triggered.
Using microwaves makes the system more robust and avoids false alarms. Microwaves cannot be changed by different temperatures in the layers of air in a vehicle left in the sun for example.
The sensors are powered and grounded via the central electronic module (CEM).