This sounds like a bit of a nightmare. We can think of two possible options - a dash cam with parking mode and/or a trail camera. A trail camera (which are usually used to record discreet footage of wildlife) can be hidden inside, or outside the car, and pointed in the direction of the side it's usually keyed. The bonus of this is that it's cheaper than a dash cam and doesn't need to be plugged in overnight. Depending on the age and condition of your car's battery and whether the electrics stay on when the ignition is off, a dash cam left plugged in can flatten a car's battery. Some dash cams offer parking mode, which means the camera turns on for a few seconds when it detects movement. The Nextbase 222 is about £55 and offers Intelligent Parking Mode. If you're worried it will drain your car's battery, you can opt to plug it into a portable power bank rather than the 12v socket/USB port in the car. The only thing to bear in mind is that a dash camera might be easy to spot and you might not actually capture the offender. In our opinion, if possible, trying to hide the trail cam might yield better results when it comes to seeing who the culprit is.