This unit is tough, dependable and power-packed with features. The DVR20 is designed specifically for mobile video, transit vehicles or remote covert video vehicle applications. The 4 camera input is paralleled with an audio input (audio version) and a 4-zone alarm that can be connected to turn/brake signal relays, door contacts, emergency exits/equipment, motion sensors, etc. Recording can be set to overwrite old footage so that a continuous record of past events up to 12 months is always accessible. Recorded video is easy to review by date, time, alarm/event and quick with incremental fast-forward times of 2x, 4x and 8x speeds. The DVR 20 can be controlled directly with on-screen menus or the included wired remote control. Not only is this unit shock-absorbing to with stand the rigors of mobile applications but is also very compact -- the small half-size chassis is just 7.5" wide x 3.5" tall x 10.5" deep. Comes with a removable /lockable hard drive bay and connection for a second external 120GB hard drive. Operates on 12 volts DC. DVR security