Mobile DVRs have anti-vibration technology to protect the device from bumps and normal movement a vehicle may endure and ensure video quality. More advanced mobile DVRs include a GPS (which can be built-in to the device or external) so location and speed information can overlay the video. Mobile DVRs can be programmed to begin recording at multiple types of events, such as: starting the vehicle, alarms, doors opening (like in buses and bait cars), signals (left/right turn), speed, siren activation, and more. This requires more inputs than a typical DVR might have. Mobile DVRs are available as 1 or 4-channel units, meaning you can only have up to 4 cameras per unit. Also, mobile DVRs are only available in analogue models (traditional DVRs are available in IP and HD-SDI models as well.