Yesterday I passed through the same screening set up 3 times in an hour and got 3 different results.

I was in McAllen (MFE) and went straight though screening no problem. I walked through the portal with no alarms and my bag went through the belt OK.

I then discovered we had a 90 minute delay, so decided to go eat landside. A few fajitas later, I went through the same lane (they only have one) and this time, I set off the alarm on the portal, but again my bag was deemed to be OK.

Almost immediately I discovered I'd left my book in the retaurant so went straight back out, picked up book, went back through. This time, I passed again, but my bag had something in it that the previous two scans had been happy with, but this time necessitated a hand search. (It turned out to be a laprtop power cable in a winder).

The inconsistency in the process worries me. Someone needs to convince me that this whole rigmarole would pick something up if someone tried to get it through.

Incidentally, whoever thought of the system where you can buy liquids airside, but can't take them on the plane must have several screws loose. It strikes me as pointless (as all liquids bought airside will already have been screened) and unenforceable.