IN THE BOX: You will receive an In-Line telephone sound amplifier with a strobe light that amplifies ringer volume from the corded telephone for the hearing-impaired to recognize the call!

In order to help his friend prepare for a talk at DEFCON this weekend, [Craig] built an IR photodiode amplifier circuit ... These sensors are there to tell the phone whether the phone is being ...

We’re talking of course about the carbon microphone amplifier, a piece of telephone technology which ... below the break we see a variety of the devices, and even hear them in action sounding ...