Remotely immobilization is a performance of a tracker physically disable the engine powering, it is also known as engine/fuel cut-off.
A tracker executes such an operation based on a remote command, which can be made from a phone number or tracking software it is connected to. While only the phone number or the user account registered as the administrator has the authority in enabling it.
The exact command format is shown on the user manual of products.
Based on a command given by the administration, and the tracker responds a positive confirmation to such a command, the immobilization would still not be executed at once, if the instant vehicle speed is not less than 20km/h. It would be executed at once when the speeds reaching to the trigger range.