1.Easy Installation Additional Installation work is not needed because the 2-wire cable and box of existing door phone can be used. 2.Free Voltage A specially designed transformer allows you to use under any voltage condition from AC 110~250V. 3.Compact Infrared LED As the infrared LED is compactly designed,it can be used at night,or in dark places without any extra lighting. 4.Extensions(Additional Monitors): Up to 2 monitors with 1 camera is possible. 5.Easy Monitoring Watching and communicating with outdoor visitor over handset. Door release Can be combined with electric lock (optional).