aps —
ThinkPad Active Protection System accelerometer
The aps driver provides support for several sensors
  found in some ThinkPad laptops.
The sensors currently exposed via the
    envsys(4) interface are:
The aps driver first appeared in
  OpenBSD 3.8 and was then ported to
  NetBSD 5.0.
Few issues can be mentioned.
  - The apsdriver does not maintain state and
      subsequently does not take evasive action when it thinks the hard drive is
      in danger. Possible actions would include spinning down the hard drive in
      case excessive tremor is detected by the sensors.
- The Y axis on X40 and possibly other models seems to be inverted. It is
      unknown how to distinguish between different versions of the accelerometer
      to compensate for this in the driver at this time.
- The sensor values are refreshed every 0.5 seconds. Because no protection
      measures are taken, this is unnecessary and may have a negative effect on
      battery life.
- As IBM provides no documentation, it is not known what all the available
      sensors are used for.