With this one, we will be assigned a position somewhere likely to be attractive to bats on the site (I think that there will be 14 of us tonight, so 14 points) and then sit there with a bat detector for 90mins or so from around sunset.

You can simply position detectors and recorders alone, without people, but they are expensive and it is best to have someone with them - you also get to see the bats as they pass and can do some of the ID there and then.

These days we record the output from the detector for later analysis of the ultrasound and a lot of that can be done automatically, using AI, but humans still need to confirm the exact species. Once you have your ear in, though, you can recognise a lot of the calls (stepped down to the range that humans can hear) 'live' as you hear them, but a lot of the myotis family of bats are very similar and need further ID, through sonograms and actual visual ID, to be certain.