Construction of Stealth Telephone Screener

The stealth telephone screener was specially designed for automatically screening the calls from telemarketers.

The screener works by answering the phone call first and playing a brief greeting and then determining if the caller is an actual person or not. It will hang up if it detects that there is no one on the other side of the telephone for about 5 seconds or when there is continuous response longer than 10 seconds, without the user picking up or being disturbed. It will play a second greeting otherwise, where the ringer gets activated while a ringing signal to the caller is played. The screener stops ringing and releases the line once the user picks up any phone on the same line.

The callers will not be aware that they are being screened during the call and this does not require the stealth telephone screener to obtain any special code. A built-in ringer is used by the screener to alert the user to reply to the call as the screener plugs into an ordinary phone line. A PIC16F872 is used to build the system since it has built-in PWM output and 10-bit A/D converter.