An electronic control unit used in, e.g., a towing vehicle includes a processing device configured to determine an initial electrical load of a trailer system, detect changes in the electrical load, and generate an alarm signal if the electrical load is substantially different from the initial electrical load. A method includes determining an electrical load of a trailer system prior to arming a vehicle alarm system, detecting changes in the electrical load after arming the vehicle alarm system, and triggering the alarm system if the electrical load is substantially different from the electrical load determined prior to arming the vehicle alarm system.