system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't they just instal a giant heat scanner (?) for all trucks to go through at Calais to easily detect migrants?
gpt
A infra red scanner can only look at the outside of the truck. Some trucks will have been out in the sun, others in the shade. Some cargoes will hold the heat more than others.  So readings will be all over the place and it won't give any useful information.