Some of the Android OS versions have a bug which stops the sensors such as the accelerometer recording when the screen lock is on.
The bug has been submitted but has not been fixed in all instances
http://code.google.com/p/android/issues/detail?id=3708
http://code.google.com/p/android/issues/detail?id=11028
Below is a list of Phones and OS versions the do and don’t have the bug + some are reported to be intermittent.
| Bug | No Bug | Intermittent |
| Motorola Milestone – 2.1 | Google Nexus One – 2.2 | Google Nexus One – 2.2 |
| Nexus One – 2.1 | T-Mobile G1 – 1.6 | |
| HTC Desire – 2.2 | Google ION – 1.6 | |
| HTC EVO 4G – 2.2 | ||
| Motorola Droid – 2.2 | ||
| HTC Eris – 2.2 | ||
| Droid Incredible – 2.2 | ||
| HTC Legend 2.1 | ||
| HTC Wildfire 2.2 |
Update: There are a couple of workarounds that i have found
The first works for all phones but is a drain on the battery and involves keeping the screen on all the time. It changes the timeout of the screen to a higher number:
http://stackoverflow.com/questions/1114270/android-screen-timeout
The second seems to only work on some phones such as the Milestone and Droid which registers the sensor, then un-registers the sensor when the screen is off and re-registers the sensor. Long winded but if it works…