Hacker News Reader

I think that is due to the thickness of a laptop compared to an ipad and some x-ray machines not being powerful enough.

One time I've had to take out my tablets, out of my bag and out of their case even.

No, luggage X-rays are extremely powerful, think 120kV or higher. They can easily penetrate inches of steel on the low end.

Some (older) laptops were sandwiched between thick metal panes, for EMC and mechanical reasons

Probably not very transparent to x-rays

Completely transparent as far as a luggage X-ray is concerned, they're very high power because they don't have to care about exposure limits like medical imaging would. They usually have multiple attenuators and detectors so they can do neat tricks like detection of organic materials.

But they usually can't detect an organic material behind a varying thickness metal plate.

And metal in laptops is often varying thickness (either due to the design, or poor manufacturing tolerance), hence the concerns that organic explosives can be hidden in their "xray shadow".

Reply on news.ycombinator.com