Back in the late 1980s when I was a teenager I found plans and built this little circuit with a LED that would light up if someone else in the house was trying to listen in on my phone calls. More than one phone off the hook... LED lights up.
Good project for a comparator chip! Just set the trigger threshold slightly below the off-hook voltage for your extension and it shows when another local phone is also off-hook. Only works locally though, and will not let you know if your phone is tapped, or if a nosy operator or phone company technician is listening.
A long time ago, I helped a co-worker tap his own phone because he suspected his wife of cheating. I gave him a device that would connect to a phone line, activate a cassette recorder when any phone went off-hook, and record the audio. He ended up getting evidence for a divorce shortly afterward.
The "butt set" phones that telco field techs have will let you connect to a line and monitor a call without affecting the voltage, so the comparitor/LED doesn't ensure privacy beyond your family extensions. I still have an old one (with a dial). It's also useful to find the right pair with a flicker test set. I still have a few of those too.
Sometimes a field tech needs to access the CO and will find an unused line on a nearby demark. Long after my phreaking days had passed, a friend of mine had connected a DTMF decoder to his phone line (AC coupled, so it was undetectable). One day he looked at his logs and found that he had recorded a session between a field tech and the CO. The phone number and access codes were his for the taking! Fortunately for the phone company, my friend is mostly a trustworthy law-abiding guy.
anonymousiam|2 years ago
A long time ago, I helped a co-worker tap his own phone because he suspected his wife of cheating. I gave him a device that would connect to a phone line, activate a cassette recorder when any phone went off-hook, and record the audio. He ended up getting evidence for a divorce shortly afterward.
The "butt set" phones that telco field techs have will let you connect to a line and monitor a call without affecting the voltage, so the comparitor/LED doesn't ensure privacy beyond your family extensions. I still have an old one (with a dial). It's also useful to find the right pair with a flicker test set. I still have a few of those too.
Sometimes a field tech needs to access the CO and will find an unused line on a nearby demark. Long after my phreaking days had passed, a friend of mine had connected a DTMF decoder to his phone line (AC coupled, so it was undetectable). One day he looked at his logs and found that he had recorded a session between a field tech and the CO. The phone number and access codes were his for the taking! Fortunately for the phone company, my friend is mostly a trustworthy law-abiding guy.