Thousands of British tourists are still waiting to come home from Egypt's Sharm el-Sheikh after flights to the UK were suspended this week.
It's after fears the Russian plane crash was caused by a bomb on board the aircraft.
Professor Nick Bowring of Manchester Metropolitan University has researched airport X-ray imaging software and body scanners in the UK.
He says operators mostly look for colour codes and "unusual shapes".
Airport scanners create a 3D image of what's inside each bag.
"It goes through an automated X-ray analysis. These machines are very sophisticated now, they illuminate the bags from various angles with various energies of X-rays," Professor Bowring explains.
"All the different materials are represented with different pseudo colours.
"Metal, for example, tends to come out blue; organic material tends to come out orange; lighter metals tend to come out green.
"That can be interpreted automatically by fairly advanced software which says this bag has maybe an undue amount of metal or organic material."
Scanner operators will be looking for "unusual shapes in there, lots of wires, that sort of thing".
"Normally luggage is mostly filled with clothes and you might have the odd laptop and batteries."
Something like a bomb would likely show up as a lump of organic material.
"High explosives tend to come out orange on the scan. It could be a bottle of a water but a different shape might indicate high explosives."
Professor Bowring says some airports also have CT (computed tomography) scanning technology, similar to scanners found in hospitals.
"It 'slices through' the luggage. So if anybody's in any doubt they can take a slice every few millimetres through and have a close look at that."
Threat image projection
Technology aside, scanner operators are kept on their toes by something called threat image projection.
"They'll add an object into the X-ray image that is a threat, like a handgun or something like that, and they'll test the operator's ability to find it.
"That happens on a routine basis. You can manipulate the X-ray image remotely, add in another object that is a threat and see if the operator is picking it up."