Read the links and article referred to in the last message. Much will become clear to you. You don't need any special plug in, nor do you need any particular scanner. If you know the frequency the tones are sent on, you're half way home.
You should be a bit careful about referring to 'pager tones'; it's somewhat misleading, because someone might think you were trying to after a POCSAG type signal, and that's not true in this case. Saying 'toneouts' is far less confusing. 73 Mike