Does anybody know if there are gadgets to monitor all calls, better still if it has recording capability, for my fixed line telephone?

After having had two maids run away, I am paranoid about my third employee following suit, more so when I found two local addresses in her hand writing scribbled on a piece of paper torn from her notbook.

I guess such a recording system will be activated only when the line is active, unlike video where the viewer has to sit through the whole show only to find no incriminating evidence. And it should be much cheaper too.