AHD video door phone

AHD video door phone is a new kind of video door phone introduced in about 2017. The conception of AHD is from CCTV system. 

Before AHD video door phone released, doorphone image resolution unit is TVL, for example 420TVL, 600TVL, 720TVL, 800TVL etc. 800TVL is about 0.3MP. You can see the the resolution is low. However, it doesn't matter a lot in video doorphone. Doorphone system only need to get clear photo in 1-3 meters range. User only need to see who is calling and decide to unlock the door or not. So that it doesn't requires high resolution. 

However, in recent year, video door phone also integreated CCTV camera system, and video door phone also can be connected to DVR, that makes high resolution is important. In this case, AHD 720P, 960P, 1080P were introduced to video doorphone system. 

AHD 1080P monitor compatible with 720P and 960P outdoor station(or camera), while 720P monitor not support 960P or 1080P outdoor station(or camera).