Pulse Dialing - Tapping

Tapping

It is possible to trick a phone system into thinking that a rotary dial is being used. To do this, one finds the little button, switch, or hook that is pushed down when the handset is hung up. The switch is then tapped the corresponding number of times at approximately ten taps per second to "dial" the corresponding number (i.e. 1 tap for the digit 1, 2 quick taps for the digit 2, and so on. The pulse dialing rules of Oslo, Norway and New Zealand are an exception; see above). This method can be used when the standard keypad or rotary dial cannot be used although the chances of dialing the wrong number are higher.

In the UK it used to be possible to make calls free of charge from coin-box phones (payphones) by tapping the switch-hook. A person caught tapping could be charged with 'abstracting electricity' from the GPO (several cases of dishonestly using telephones without paying were prosecuted under this offense). As the coin-box dial was designed so that toll (0) and emergency service (999) calls could be made without inserting coins, it was possible to dial the digits "0" and "9" without tapping the switch-hook.

In popular culture, tapping was used in the film Red Dragon as a way for prisoner Hannibal Lecter to dial out and circumvent a phone with no dialing mechanism. This method was also used by the character 'Phantom Phreak' to call 'Acid Burn' when taken to prison in the film Hackers.

Phone locks were sold to prevent unauthorized use of telephones. These attached to the rotary dial and prevented rotation. Tapping was difficult, but not impossible, on standard phones, because the line switch had a slow return characteristic, designed to stop it from accidentally dialing when the handset was not sitting correctly in seat, and to stop it accidentally being triggered when a call was in progress. After the national phone systems were deregulated in many countries, cheaper handsets became available and these cheaper handsets often did not have the slow-return characteristic on the line switch.