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!