... ,our wireless video door phone was welcomed by lots of customersFunction feature:1)Transmission distance over 300meters (free lane ... channels,frequency-hopping technology,super eror- correcting capability ,so the conversation is very stable8)Untrashort bulit-in antenna design ... ZhongshanRoad,HeTanGang,Beizha,Humen,Dongguan,Guangdong, China check out the high tech video door phone ,rock and roll set up