none Indoor phone ---VT689 Basic Parameter: Display screen: 4 inch B/W flat CRT or TFT color Resolution: ≥400TV lines Video signal: 75V 1Vp-p(CCIR OR NTSC) Power voltage: DC 16-18V Power consumption: standby state 0.5W; working state 12.3W Audio frequency: 0.5W Dimension: 196(W)?60(H)?0(D) Function: 1. Hands free style indoor phone with function of dual talking with outdoor station, intercom and remote unlocking. 2. Can supervise the front door situation at any time 3. Can adjust the contrast and brightness. 4. Intercom function is available. 5. All kinds of the indoor phones and outdoor stations are totally compatible