How can I scramble a listening device? ?

How can I scramble a listening device? ? I have a horrible neighbor, an elderly lady 75 years old, who listens to my phone calls anyway she can. I caught her before, with a baby room monitor, and a "Listen Up" in her ear. Her porch is just a few feet from my living room (condos). She is constantly snooping, and now, every time I get a phone call, I can clearly hear her picking up, and listening. What to do?

Thanks, if you can help!

PS: I've heard an F.M. radio, by my glass window can scramble her ability to do this. Anyone know?