# When a mobile phone is off, what does it continue to do? **URL:** \ **Category:** Factual Questions\ **Created:** [April 24, 2014, 6:28pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880 "2014-04-24T18:28:24Z")\ **Posts on this page:** 2\ **Page:** 3
**Author:** ![Little\_Pig](https://avatars.discourse-cdn.com/v4/letter/l/c57346/32.png) [@Little\_Pig](https://boards.straightdope.com/u/Little_Pig)\ **Post date:** [May 1, 2014, 9:12pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/41 "2014-05-01T21:12:20Z")
[Cell phone jammer caught.](https://www.yahoo.com/tech/a-florida-resident-drove-around-with-a-cellphone-jammer-84369099229.html) The mention the Antenna System & Supplies Inc.’s TRJ-89 jammer, which is able to block cell service within a 5 mile radius. That should quiet things down. ---
**Author:** ![Digital\_is\_the\_new\_Analog](https://avatars.discourse-cdn.com/v4/letter/d/a88e4f/32.png) [@Digital\_is\_the\_new\_Analog](https://boards.straightdope.com/u/Digital_is_the_new_Analog)\ **Post date:** [May 2, 2014, 2:14am UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/42 "2014-05-02T02:14:24Z")
> [@AaronX](#): > > I’ve seen phones keep their time even with the battery removed for ~1 minute. There is usually a supercap or coincell battery that powers a very low power 32k clock, which basically keeps track of time while the device is “off.” > [@md2000](#): > > My experience with iPhone 3GS is it says “no SIM card” and does not even try to find a carrier; since the process appears to be “find carrier, pass on SIM info, see if carrier is the SIM originator or a partner and validates”. Last I checked, it was a requirement by US law that phones emergency camp on a network even without a SIM card. This allows you to call 911. So even when it says no SIM, it is looking for and camping on a network. [Previous page](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880.md?page=2)