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Topic # 159853 15-Dec-2014 09:56
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Obviously if I take the battery out it is but .... if my smart phone (GS4) is really off when 'shut down' how does it detect a long press of the main key as a signal to switch on?  Surely some part of the phone activated and monitoring the key for a long press?

No particular point to this question I'm just curious.






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  Reply # 1197606 15-Dec-2014 10:32
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Capacitor? 555 timer?

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  Reply # 1197618 15-Dec-2014 10:48
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It's a good question. Especially for phones like the iPhone where the battery cannot be removed by the user.





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  Reply # 1197666 15-Dec-2014 11:59
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Yes, there is always some circuitry (e.g. a Real Time Clock) which is 'alive', even when the power is 'off'. That applies to all kinds of appliances and computers and so on. Often, this RTC circuit (which may be a microprocessor or microcontroller) will have life-or-death power over the main processor, and will wake it in response to receiving a 'power-on' signal from the user.

Typically a phone will have a super-cap or similar to keep power on for stuff like a RTC while the battery is changed. I don't know how long the super-cap would last, but I'd guess it would be minutes rather than hours.

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  Reply # 1197675 15-Dec-2014 12:09
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If you watch TV then you'd have the impression that all phones are GPS trackable even when off! :-)

But yes some parts are still live while there is a battery in it, as you mention the process to turn it fully on when you press the power button, the clock (so it can keep time and wake the phone on an alarm) and probably other gizmos as well.

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  Reply # 1197687 15-Dec-2014 12:26
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Skynet...once activated it cannot be shut down!!!




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  Reply # 1197733 15-Dec-2014 13:40
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There is a special part that monitors the power button, both to power on, and to force a reset of the main processor on a super long hold of the button for when the main processor locks up.




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