On Google's specs page for the new Nexus 5, the Nexus 5's built-in sensors are listed as:


Proximity/Ambient Light

(Click "View Full Tech Specs" to see that list)

Looking up Hall Sensor on Wikipedia, it seems to be some sort of magnetic sensor, but it's not the compass because that's listed separately, and none of the example uses on the page seem to make much sense for a smartphone application.

What is it, and what is it useful for?

  • 1
    This article and this other article seem to imply that the the compass is (or can be?) a Hall Effect Sensor. But that confuses me, since - as you mentioned - the compass is mentioned separately on the Sensors list.
    – dotVezz
    Nov 7, 2013 at 14:06

6 Answers 6


As you've found out, a Hall sensor detects a magnetic field. It could be that in this case it's referring to a sensor for a magnetic cover, like those in the Nexus 7 and Nexus 10. Such sensors detect the proximity of a magnet embedded in the cover or case for the device, in order to automatically turn the screen off when the cover is closed.

That would be unusual, as that kind of magnetic switch is usually a simple reed switch, which wouldn't normally be described as a Hall effect sensor. A Hall sensor would give more data about the strength of the magnetic field, which could be used by software to detect the opening or closing of the case more reliably. However, I've not seen any claim that the Nexus 5 has such a switch anyway, which is much less common on phones than tablets.

Another (just as far-fetched) guess is that it's related to the wireless charging capability. It could be that the Hall sensor is specifically there to locate the wireless charging point in relation to the phone's position.

  • You mention that you haven't seen any claims that it has a sensor for magnetic covers. Perhaps this may be evidence that it does?
    – dotVezz
    Nov 7, 2013 at 17:33
  • @dotVezz Ah yes, so it does. It could well be that, then.
    – Dan Hulme
    Nov 7, 2013 at 20:33
  • 1
    Some devices also use a similar sensor to determine whether they are plugged in to a charger or a dock, such as a car dock. Apr 11, 2014 at 5:22

Just a guess here, but the Samsung S-View flip cover knows when the cover is attached and runs only the part of the screen that is veiwable in the small window. Maybe it is the same for the Nexus.


Reed switches are bulky and have mechanical contact bounce. They require a relatively strong field to do their thing. OTOH, Hall sensors have none of these shortcomings, BUT they are powered devices.


I know the question was about the Nexus, but from Samsung's website, "Hall Sensor: Recognizes whether the cover is open or closed."


Perhaps the sensor is included on smartphones without a cover in order to support aftermarket smartphone cases which may include a small magnet on the cover to signal to the phone whenthe cover is closed.


VR headsets has a magnetic button in it. Hall sensor comes very handy since we cannot access the display.

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