SpiderRoi uses proximity and orientation sensor.
If your device isn't close to you (or object) and slope of device is changed, SpiderRoi let you know it by sound and vibration.
*. The use of this App
1. Prevent losing
If your device fell unwittingly from your pocket and nothing in the range of proximity sensor, alarm rings.
(You may save hundres bucks by a dollar)
2. Attention on you
You can get attention easily in an emergency by just getting the device out of your pocket.
If you need attention but can't (or don't want to) shout out, you can use this App.
3. Fake call
Set 'Alarm delay' to 30 or 60 sec.
You can ask to be excused from the table when alarm rings in 30 or 60 sec.
4. So on
* Alarm may be worked rarely if slope of device is changed. (even if the device is in your pocket.) but it isn't App's bug.
The reason is that some proximity sensors have different range of recognition by size and material of objects.