https://devzone.nordicsemi.com/f/nordic-q-a/41228/51822-no-wakeup58122,NO WAKEUP, sometimes no wakeup,code as below: void Power_Down(void) { NVIC_EnableIRQ(RTC0_IRQn); if(SYSTEM_MODE_NORMAL == gSystemPara.body.mode) { NVIC_EnableIRQ(GPIOTE_IRQn); } NRF_CLOCK-&gt;TASKS_HFCLKSTOP = 1; if(WAKEUP_FROM_RTC0 == gWakeUpModeen-USTelligent Community 13Wed, 05 Dec 2018 12:21:20 GMThttps://devzone.nordicsemi.com/thread/160366?ContentTypeID=1Wed, 05 Dec 2018 12:21:20 GMT137ad170-7792-4731-bb38-c0d22fbe4515:d2971a97-46e9-4414-93b2-373c024986f6Einar Thorsrud<p>Hi,</p> <p>I do not see that you start the LFCLK in the code you have pasted. The RTC needs the LFCLK, so you will not get any RTC events when it is not running.</p><div style="clear:both;"></div>