‘But there is a difference between recognising AI use and proving its use. So I tried an experiment. … I received 122 paper submissions. Of those, the Trojan horse easily identified 33 AI-generated papers. I sent these stats to all the students and gave them the opportunity to admit to using AI before they were locked into failing the class. Another 14 outed themselves. In other words, nearly 39% of the submissions were at least partially written by AI.‘
Article archived: https://web.archive.org/web/20251125225915/https://www.huffingtonpost.co.uk/entry/set-trap-to-catch-students-cheating-ai_uk_691f20d1e4b00ed8a94f4c01
... Then they locate the ones inside the room and deal with them accordingly.
Guessing you didn't understand the triangulation part of my suggestion, but you can detect the direction of the source of electromagnetic signals (which is what wifi, Bluetooth, and the cellular signal all are). If you have two sensors that can detect direction, then you can use those to get two lines pointing at the source, which will be where those two lines meet.
Though if one person was moving around with a directional sensor, it would also be able to lead to the location of the device. But having two to triangulate with would allow for quick automated filtering of all the outside devices detected.
They could also build a faraday cage around the exam area to prevent any outside signal from getting in, at which point they know any detected signal is coming from within. Plus they might catch people just by looking for visible frustration at not being able to connect to the internet.