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A sleeping ESP needs a reason to wake. The two classic triggers are a timer that counts down and a pin that senses an event. ⏰

A timer wakeup is perfect for regular jobs, like reading a sensor every ten minutes. The chip sleeps, then wakes right on schedule.

Timer values are in microseconds. For ten minutes you write 600 seconds times one million, so picking the right zeros really matters.

An external wakeup reacts to the real world. A motion sensor or button can jolt the chip awake the instant something happens.

The ext0 source watches a single RTC pin. You choose the pin and whether a HIGH or LOW level should trigger the wakeup.

Need several buttons? The ext1 source watches a group of RTC pins at once, waking when any of them hits the chosen level.

Not every pin can wake the chip. Only the special RTC pins stay alive during deep sleep, so wire your trigger to one of those.

You can arm a timer and a pin together. The chip then wakes on a regular schedule or immediately if an event interrupts the nap.

After waking, ask the chip what happened with wakeup_cause. Then you can run different code for a timer versus a button press.

Compare the cause against known sources to branch your logic. A timer might mean read a sensor; a pin might mean send an alert.

Always set your wakeup sources first, then call sleep last. Arming after the sleep call is pointless because that line never runs.

Pick the right wakeup for the job.

Use a timer for scheduled jobs and an ext pin for real-world events. Arm sources before sleep, then check the cause to branch on wakeup. ⚡