We encountered this problem
There was a large carpark near one of our installations and an empty building nearby
The criminals had setup a jammer on 433.92Mhz to operate between 5pm & 10pm weekdays & all weekend
We operate monitoring equipment on that frequency and every day between 5 & 10pm and the weekend, we couldn't recieve any signals from the equipment.
I ended up sitting outside with a portable radio scanner for 2 evenings to figure it out, we contacted the police and the problem went away the next day.