Best People Detecting Proximity Sensor

I am looking for a rangefinding proximity sensor for detecting people at 25'-30'. I thought an ultrasonic sensor was my best bet, but due to the absorbtion effects of clothing I need to change gears.

Good pair of eyes needed 8)

I don’t about a sensor tho …

There are some types of intrusion protection radar or more precisely well tuned 10 GHz motion detectors that are/were available. I worked with one in the early 90’s that
was good for about 100 meters. Perimeter denial deices, I think they were called. Cost was never mentioned but I’d estimate those sold for 3 figures… Big 3 figures.

Bob