How to prevent jammers

I recently noticed that my wifi cam dint pick up my car service people towing my car. This happened previously with the same guys. I am not sure if they are using jammers; how to check this and is there a way to prevent this?

It is illegal to use jammer.
Just wifi is not working. Your sd card should still be recording.
Do U have missing gap in your sd card?
If so, it is something else with card problem.