# Smart phone question **URL:** \ **Category:** Factual Questions\ **Created:** [December 9, 2018, 4:18am UTC](https://boards.straightdope.com/t/smart-phone-question/825836 "2018-12-09T04:18:38Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [December 9, 2018, 4:18am UTC](https://boards.straightdope.com/t/smart-phone-question/825836/1 "2018-12-09T04:18:38Z")
I noticed that when my son’s smart phone has a blank screen, it comes to life when your hand moves close. It is pretty sensitive and senses a hand just off to the side of the screen even. What is it using to sense something close? Dennis ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [December 9, 2018, 4:37am UTC](https://boards.straightdope.com/t/smart-phone-question/825836/2 "2018-12-09T04:37:32Z")
There is not enough info in the OP to know what is happening. That said some new smartphones have face recognition as a means to unlock the phone. The phone has a few sensors on the front as well as a camera on the front. The sensors detect movement and the camera has a look. If it sees your hand it does not register that as something to allow access so you see a blank screen Working as intended. ---
**Author:** ![Beckdawrek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beckdawrek/32/3647_2.png) [@Beckdawrek](https://boards.straightdope.com/u/Beckdawrek)\ **Post date:** [December 9, 2018, 4:48am UTC](https://boards.straightdope.com/t/smart-phone-question/825836/3 "2018-12-09T04:48:18Z")
My phone does that. I am not sure why. I’ve tried to turn it off, no luck. I can also shake it to answer it, it’s kinda dumb. But I’ve gotten use to it. Well, it does that shit when I can find it. They need a thing on it to make it easier to locate. I have a few alarms set so maybe I’ll hear it and find it that way. Hey, it could happen. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [December 9, 2018, 4:52am UTC](https://boards.straightdope.com/t/smart-phone-question/825836/4 "2018-12-09T04:52:28Z")
Both iPhones and Android phones have a “find my phone” feature where you can tell the phone to sound an alarm by issuing a command on their web site. ---
**Author:** ![Baron\_Greenback](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/baron_greenback/32/48_2.png) [@Baron\_Greenback](https://boards.straightdope.com/u/Baron_Greenback)\ **Post date:** [December 9, 2018, 5:01am UTC](https://boards.straightdope.com/t/smart-phone-question/825836/5 "2018-12-09T05:01:21Z")
> [@mixdenny](#): > > I noticed that when my son’s smart phone has a blank screen, it comes to life when your hand moves close. It is pretty sensitive and senses a hand just off to the side of the screen even. What is it using to sense something close? Infra-red proximity sensor, most likely. The primary use case for this is to detect when the phone is right next to one of your ears. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [December 9, 2018, 5:21am UTC](https://boards.straightdope.com/t/smart-phone-question/825836/6 "2018-12-09T05:21:00Z")
[The proximeter, ambient light sensor, or both](https://gizmodo.com/all-the-sensors-in-your-smartphone-and-how-they-work-1797121002). ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [December 9, 2018, 2:02pm UTC](https://boards.straightdope.com/t/smart-phone-question/825836/7 "2018-12-09T14:02:24Z")
> [@markn\_1](#): > > Both iPhones and Android phones have a “find my phone” feature where you can tell the phone to sound an alarm by issuing a command on their web site. Most of us just ‘dial’ the number…? ---
**Author:** ![SigMan](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@SigMan](https://boards.straightdope.com/u/SigMan)\ **Post date:** [December 9, 2018, 2:09pm UTC](https://boards.straightdope.com/t/smart-phone-question/825836/8 "2018-12-09T14:09:58Z")
> [@Baron\_Greenback](#): > > Infra-red proximity sensor, most likely. The primary use case for this is to detect when the phone is right next to one of your ears. This and the screen blanks to conserve the battery. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [December 9, 2018, 2:44pm UTC](https://boards.straightdope.com/t/smart-phone-question/825836/9 "2018-12-09T14:44:24Z")
> [@bob\_2](#): > > Most of us just ‘dial’ the number…? Yeah, if you have a second phone handy. Sometimes all you have is a computer. ---
**Author:** ![filmstar-en](https://avatars.discourse-cdn.com/v4/letter/f/50afbb/32.png) [@filmstar-en](https://boards.straightdope.com/u/filmstar-en)\ **Post date:** [December 10, 2018, 8:59am UTC](https://boards.straightdope.com/t/smart-phone-question/825836/10 "2018-12-10T08:59:41Z")
Those proximity sensors are used to switch off the screen when you hold your phone to your head. It stops your ear touching the screen and maybe interfering with the call. It is easy to accidentally touch mute and then your caller can’t here what you say - this is very annoying. In the early days of smartphones some third party phone cases interfered with the proximity sensor. These days they have holes in the right places. I guess your phone uses the proximity sensor to save power by switching off the screen when it is not in use. I would guess it also other sensors go give additional clues to establish whether it is in use. These gadgets are full of sensors: proximity, orientation, inertia, camera, audio. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [December 10, 2018, 10:45am UTC](https://boards.straightdope.com/t/smart-phone-question/825836/11 "2018-12-10T10:45:51Z")
> [@markn\_1](#): > > Yeah, if you have a second phone handy. Sometimes all you have is a computer. Then message a friend/relative/colleague and ask them to do it…🙂 ---
**Author:** ![brad\_d](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@brad\_d](https://boards.straightdope.com/u/brad_d)\ **Post date:** [December 10, 2018, 2:01pm UTC](https://boards.straightdope.com/t/smart-phone-question/825836/12 "2018-12-10T14:01:18Z")
> [@bob\_2](#): > > Most of us just ‘dial’ the number…? That works fine if the ringtone volume is up. Google’s version of the “find my phone” feature can cause the phone to ring at full volume even if it’s on vibrate-only, and I imagine Apple’s is similar. I’ve found it useful in the past for this reason. ---
**Author:** ![Kron](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kron/32/12444_2.png) [@Kron](https://boards.straightdope.com/u/Kron)\ **Post date:** [December 10, 2018, 3:52pm UTC](https://boards.straightdope.com/t/smart-phone-question/825836/13 "2018-12-10T15:52:42Z")
> [@Baron\_Greenback](#): > > Infra-red proximity sensor, most likely. The primary use case for this is to detect when the phone is right next to one of your ears. Yep, my phone has infrared sensors, so I have my hand near it and it wakes up. I can also pass my hand over it from right to left to snooze my alarm, or left to right to shut off the alarm off.