Telephone line checker with noise filter. The TelCheck PRO is an enhanced TelCheck. It does function not only containing telecommunications circuit that detects dangerous telephone line conditions before a modem is connected, thereby protecting the modem from damage, but also with the line noise filter. Near a radio transmitter telephone wires can act as antennas which draw radio frequency interference (RFI) to corrupt data receiving over modem and interrupt your internet and E-mail connection. With TelCheck PRO the modem on your notebook computer will be completely protected and reduced the headache of internet/E-mail/Fax being interrupted by RFI. Easy to identify the polarity of the line. It tells you if the line is over current. It prevents your modem from damaged by plugging in incorrect telephone system. Easy to identify the connecting status of the line whatever it is a new installed line or existed line. Compact and easy operation. Line noise filter reduces RFI interfering.