[Update: Additional details below the fold.]

I suggested last week that Apple’s apparent move to remove security tethers from demo devices in its retail stores likely wasn’t too risky thanks to a range of hidden security measures, and we’ve been hearing a little detail on how some of these work.

Apple has long had special OS images for demo devices. You can’t, for example, set a passcode on a iOS device and then lock it, and Macs revert to their original state after a reboot.

Apple regularly tweaks these images. For example, at one time you could go into Safari and change the homepage to any site you liked; there’s now a lock-out to prevent this.

One security feature on the current display models of both iOS devices and Macs is designed to instantly render them useless if someone removes them from the store …

A source tells us that the current special OS images on demo devices include a software ‘kill switch’ which disables them when they go out of range of the store Wi-Fi. This means that Apple no longer has to use Find My iPhone to disable them manually.

Devices used for workshops have a different image to those in the main sales area. This is closer to stock than those out in the main sales area, but they still have the kill-switch to protect them from theft.

Former Apple Store staff report that special OS images came to Macs before iOS devices.

People would take photos with the demo iPhones, and we had to manually delete them all at the end of the night!

While CNET couldn’t spot any CCTV cameras in London’s Regent Street store, I wrote that I was sure they were there, visible or not, and this has been confirmed by former employees.

There are HD security cameras scattered around the store – they are just hard to spot.

This isn’t the first time Apple has removed security tethers. The company did so years ago for keyboards, trackpads and speakers, and it also experimented with removing them in the days of the iPhone 5. That wasn’t a success, with thefts shooting up, but with the safeguards now in place, such thefts should soon drop off as soon as word gets around to thieves that there’s no point in stealing them.

[Update: We’ve heard more about how the new tetherless process works: The iPhone will reset when the device is powered off and then plugged in. When removed from the Apple Store, the stolen iPhone can’t do anything but ring for Find My iPhone until the battery dies. The iPhones are also Activation Locked using iCloud as a deterrent just like customer iPhones.]