Mini AV transmitter:

The smallest wireless Av transmitter kit in the world:43 x 28.5 x 16mm. It comes w/ a same-size receiver. Four channels available! Under the application upon a wired camera , a mini-wireless system  is well established to broadcasting quality recording capability at frequency of 2.4GHz . Up to the end, the receiver can be connected w/ any AV recorder even DVR, thru which u can monitor or record anything in front of the camera over a long distance. This a perfect solution for covert surveillance at dangerous occasions.