Latest I noticed at LHR T5 was that iPads etc must have covers, including neoprene, removed before placing in the separate tray.
At some airports the pre-security signs instruct you to place mobile phones in your hand luggage, as opposed to in the tray, although I’ve never seen anyone told to put one back into the bag. This can be tricky where the security agent feeding the x-ray machine also wants to see your boarding pass, which has typically been scanned a few yards back by an automatic gate.
There’s a new term “phablet” emerging to describe phones like the Samsung Galaxy Note range with screen sizes of around 5 to 6 inches. Wonder where they will have to go!