Systems and methods for determining vehicle ignition state using a device added to the vehicle after the manufacture of the vehicle without a direct connection to the vehicle ignition line are disclosed. In a number of embodiments, a system includes a processor, a motion detector configured to detect vehicle motion and to enable the processor to obtain motion data, a Global Positioning System (GPS) receiver configured to determine location and to enable the processor to obtain at least speed data, and a radio transceiver configured to communicate with the processor. Additionally, the processor is configured to estimate the ignition state of a vehicle using at least the motion data and the speed data.