What happens to a CPAP when the power cuts mid-night?

The blower stops and airflow ends within seconds. Most machines have no battery and no alarm, so they simply go quiet. Manufacturers direct you to remove the mask if the machine stops running, because a mask with no airflow traps exhaled air.

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Medistrom Pilot-24 Lite
Simplest overnight cover
At 95Wh this covers one dry night at about 9.1 hours, which is the specific gap this page describes — the night the power cuts and nothing takes over.
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Power-draw figures for the machines below are provisional estimates, not yet our own meter readings. See how we test.

Most people who ask this have had it happen and want to know whether anything was wrong. The short version: the machine is fine, it will restart when power returns, and the part worth knowing about is the mask rather than the motor.

What the machine does

Airflow stops within seconds. There is no reservoir of pressure; the blower is the pressure.

Most machines have no internal battery and no alarm. A CPAP is not built as a life-support device, so it fails silently. Some models hold settings and usage data in non-volatile memory and simply resume — a sudden power loss does not normally erase your settings or therapy data.

No damage in normal circumstances. A CPAP tolerates an abrupt cut the way most small appliances do. The heated humidifier chamber will still be hot and stays hot for a while.

It restarts when power returns, though most units come back to standby rather than resuming airflow on their own, so therapy does not restart until you do.

The mask is the part that matters

CPAP masks are designed around continuous airflow. They have deliberate vent holes that flush exhaled air out of the mask, and that flushing depends on the machine running. With the blower stopped, exhaled air is no longer being cleared.

Manufacturer manuals are consistent on this point: if the machine stops running, take the mask off. That is standard equipment guidance rather than anything clinical, and it is in the manual for your machine — worth reading the relevant page before you need it.

Why you usually wake up anyway

In practice most people wake when the airflow stops, because the pressure they have adapted to disappears and the mask becomes stuffy quickly. That is the de facto alarm, and it is why a silent failure is less dangerous than it first sounds — but it is not something to rely on by design.

What to put in place beforehand

A battery removes the question entirely. For a single night of dry therapy you need about 65Wh, which even a small CPAP battery covers — see running a CPAP during an outage.

If you want the handover to be automatic rather than something you wake up and do, look for a power station that supports UPS or pass-through mode, where the machine runs through the battery continuously and mains simply keeps it topped up. The changeover is then invisible.

Keep the battery charged and somewhere you can reach in the dark. A charged battery in a cupboard you cannot find at 3am is not a plan.

Will a power cut damage my CPAP?: Not in normal circumstances. Machines tolerate an abrupt loss of power, and settings and therapy data are held in non-volatile memory rather than lost.
Does a CPAP have a battery backup built in?: Almost none do. A handful of travel machines accept a clip-on battery module, but a standard home CPAP has no internal backup and no alarm when power fails.
Should I take the mask off if the power goes out?: Yes — manufacturer manuals direct you to remove the mask if the machine stops running, because the vents that clear exhaled air rely on the blower being on.
Will my CPAP restart by itself after an outage?: It will power back up, but most machines return to standby rather than resuming airflow, so you have to start therapy again yourself.

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