In a very brief scene, Theo walks through a security arch on his way into the Ministry of Energy. After waiting in queue, he walks towards a rectangular archway. At his approach, two horizontal green laser lines scan him from head to toe. Theo passes through the arch with no trouble.
Though the archway is quite similar to metal detection technology used in airports today, the addition of the lasers hints at additional data being gathered, such as surface mapping for a face-matching algorithm.
We know that security mostly cares about what’s hidden under clothes or within bodies and bags, rather than confirming the surface that security guards can see, so it’s not likely to be an actual technological requirement of the scan. Rather it is a visual reminder to participants and onlookers that the scan is in progress, and moreover that this the Ministry is a secured space.
Though we could argue that the signal could be made more visible, laser light is very eye catching and human eyes are most sensitive at 555nm, and this bright green is the closest to the 808 diode laser at 532nm. So for being an economic, but eye catching signal, this green laser is a perfect choice.