The Device screen allows you to configure.
Time: Displays, and allows you to adjust, the current device time.
Screen mode: You can change these settings to affect the screen color depth so as to improve the appearance and readability of the on-screen elements. This is usually mostly beneficial on older, gray scale devices, but experimentation with your device will allow you to determine which setting is most pleasing to you.
Popup depth: If you set this to 'Max' then, upon an Alarm or Timer event, mobileCLOCK will switch the screen mode to the best possible resolution and color depth. Usually this works fine, but some devices can experience instability when the screen mode is switched at that time. If you find that your device has problems you should set this to 'Default'.
Fast wakeup: This option is available only OS5 devices, and on all other devices this setting will be hidden, and set to the default. On some devices, it seems that some device configurations do not work well with the default setting, so it is recommended that, if your device does not seem to wake up properly when an alarm happens, or if pending messages (SMS, for instance) seem to block an alarm from happening, then try changing this setting between On and Off.
PocketTunes stop: If you are using PocketTunes for your event sounds, and you find that the PT sound is not stopping properly when you cancel or snooze an alarm, then you should turn this option on to force PT to stop at that time. This will also stop any PT playback that was previously happening, so you may not want to turn this on unless necessary.
Test buttons: This will display a screen with a variety of test buttons. These buttons will be used to troubleshoot operation problems on specific devices. Many of the buttons will have no effect on most devices, but some may cause unwanted results, if used on the incorrect device. It's best to leave these alone, unless directed by the author.
Reset: This will prompt a soft-reset of the device. This is just for convenience, where it is sometimes a hassle to use the reset hole at the back of the device.