I need to add a phone/extension in one of the rooms in our small
office. It has an existing connection/extension, so it was likely
connected at one time, but is no longer active.

Background: We have a small office, with about 30 phones in 12 rooms,
and a central, small phone room. The phones have been moved around
over the years, so we have some currently non-active jacks, with
possible cables running to our central phone room.

Question: Isn't there an electronic device that I can plug into the
phone jack (connect to one end of the cable) and have it make a signal
(noise) that I can then go to the phone room and find the cable that
the signal is coming from?

Question: What is the name of this electronic device? What is this
piece of test equipment called?

Or can you suggest another way to find the correct cable?

Thank you,
Bill