Keeping in mind that I haven’t looked into this in over 20 years, back then the answer was technically yes but practically not really, or at least not well, and I’d be surprised if the answer has changed much in the intervening years. Radar has a fairly wide beam and most systems, at least at the time, would just leave it on all the time, so it would be pretty easy for a radar detector to pick up the signal while it was targeting other cars, well before the car with the detector would be targeted. This would typically give the driver time to slow down before they were targeted. By contrast, LiDAR uses a much narrower beam. IIRC the width of the beam even at some of the farthest effective distances was still about 3-feet (≈1 meter) wide or less, and the officers were trained to aim at where the front license plate would be. That meant it was quite likely that the targeted vehicle would absorb or reflect most if not all of the signal. On top of that, the LiDAR guns would only be active for a few seconds, so even if there was rogue signal that made it past the targeted vehicle there would only be a very limited window for the detector to observe it. It’s absolutely possible for the detector to pick up the frequencies being used, but more than likely if it was detecting a signal it would be because an officer was in the process of getting the vehicle’s speed so any alert would be coming too late.

Valentines work

https://www.valentine1.com/v1-detectors/