Function: Line status test DC level detection circuit and to determine positive and negative polarity Telephone ring bell signal flow detection - Power: 2* DC 9V batteries (included) - Maximum operating current: transmitter: = 20MA receiver: = 100MA - Signal transmission format: multi-frequency pulse - Signal level reported: 8vp-p - Signal transmission distance: = 3km - Package contains: 1* Transmitter 1* Receiver 1* Earphone (2.5mm tip 110cm cable length) 2* RJ45 cable (17.5cm length each) 2* RJ11 cable (16cm length each) 1* 2-in-1 alligator clips (19.5cm length) 1* manual 1* Travel bag