A chinger is a telephone
fraud device that mimics the frequency made by a pay telephone when
money was dropped into it. Putting
money in the coin slot caused a DTMF or Dual Tone Multi Frequency signal to be sent out to the central switching
box which registered it and when enough
money had been inserted into the phone would connect the call. The chinger could mimic that sound and thus produce the equivalent effect of dropping a quarter into the pay phone.
So basically, a chinger allowed the user to make unlimited free calls from certain pay phones. They could be made using a simple pocket electronic address
book sold at Radio Shack, and replacing the chip inside to alter the output sound.
They were also known as "red boxes" but the name chinger probably referred to the chiming sound it made when mimicing a quarter
drop.
Most modern pay phones no longer use the DTMF tones, rendering the chinger obsolete... but it was fun while it lasted!