Ultrasonic sensor vs mice

Hi there. I'm currently making a project for a mice trap, where I'm using the ultrasonic distance sensor to detect is the mice in the trap and then using servo to close the trap. My concern is that mice obviously can hear sounds in 40KHz frequency in which this sensor works. In fact after a bit of Google research I found that in that frequency mice send a distress signals. So the question is will the mice even gonna come close to the trap or will stay away from it? Anyone had any similar experience/projects? Alternative would be using a motion detecting sensor but I think it's minimum range for distance is still too big to make a small enough mouse trap.

I think that a mouse will avoid US noise. What about an IR light barrier?