You may have heard of an app called Accelerometer Disabler. Sometimes locking the orientation of the screen can be useful, like if you're lying in bed. This is a feature not yet integrated into WP7. The app to add it in required an interop unlock, meaning only first-gen Samsung and LG users could run it. It also would permanently disable the accelerometer once run, requiring a reboot to turn it back. A nice niche feature, but ultimately a little too unwieldy for most people. Luckily, development didn't start there and the new Orientation Lock is now available.
Like the last version, Orientation Lock will disable the accelerometer once run. Unlike the last version, however, is now available with a general dev unlock, such as with ChevronWP7
, meaning almost anyone can run it without issue. It also solves the other major problem from the past, the permanence of the disabling, by allowing a simple slider to turn the feature on and off. Unfortunately it's not a true orientation lock, meaning that the accelerometer is turned off completely rather than simply ignored by most things. This does mean that if you intend to game or use other accelerometer related features, you will need to toggle the program off, however this is vastly easier than rebooting your device every time you wish to do this. You can grab the XAP over at Windows Phone Hacker
Hopefully Microsoft will incorporate a proper feature into Tango or Apollo to make this feature more accessible. Why isn't it there already? Well, it's a matter of developer time. It's only useful in a few situations and falls low on the priority list beside a large host of other features to be implemented, such as we saw in Mango. It'll probably come eventually, but it's understandably why it's been left out so far. Building an OS from scratch takes a lot of work.