You have to collect proof. You have to locate the devices, using the suggestions I've made, both in the article and in the comments section.
People must become pro-active and fight back, not literally, but to thwart their stalker.
1. Never interact with them or give them the satisfaction of knowing you are frightened.
2. Gather proof. I cannot say this often enough.
3. Ensure he cannot break in. Make sure there are security locks on windows and doors.
4. Make technology work in your favor. These days you can install apps on your phone that work with cameras in your home so you can see who comes to the door, wherever you happen to be.
5. Do install your own cameras all over your home. If you can get a recording of a stalker entering your home, you have proof.
6. Purchase a bug scanner and use it. A cash layout of $20-$60 is a low price to pay for peace of mind.
7. Keep a record of everything - even if you don't think it's that important. Silent phone calls, strange vehicles lurking outside, people hanging around, etc.
8. Keep a loud whistle on you at all times. If you get any weird calls, blow the whistle as loud as you can down the phone. Also always carry a rape alarm.
It's your life; you need to protect it and get this person out of it. Meanwhile, take commonsense precautions, but do not allow them to ruin your life. You can be cleverer than them.