A red status indicator almost always means the AED has failed its automatic self-test and should be treated as out of service until the fault is cleared. The important exception is that red does not mean the same thing on every device. On a HeartSine samaritan PAD a brief red flash during the Sunday self-test is normal. On Philips HeartStart units a fault shows as no light at all, never red. Before you act, confirm what your specific model is actually telling you.
This guide decodes the status indicator for each major AED brand, explains the three cases where red is not a fault, and sets out what to check and in what order. It is about reading the indicator correctly. If you have already confirmed a genuine self-test failure and need the brand-by-brand fix steps, those are in the guide on what to do when an AED self-test fails.
What the status indicator is actually reporting
Every modern AED runs an unattended self-test on a fixed schedule. The indicator on the outside of the case is a summary of the most recent result, nothing more. It is not a live reading, and it is not a measurement taken at the moment you looked at it.
That distinction matters more than it sounds. A device that failed its test four days ago has been showing a fault for four days, and a device that passed its test yesterday can have developed a problem since. The indicator tells you the outcome of the last scheduled check, which is why the self-test interval in the table below is as important as the colour.
Status indicator meanings by brand
The ready state, the fault state, the sound and the test schedule all differ by manufacturer. The table below is drawn from each manufacturer’s own operating instructions.
| Device | Ready | Needs attention | Sound | Self-test schedule |
|---|---|---|---|---|
| ZOLL AED Plus | Green check mark in the status window | Red X in the status window | Audible alert with the red X | Every 7 days by default, configurable from 1 to 7 days. Software 5.32 and above also runs a monthly test |
| Philips HeartStart OnSite (HS1) | Blinking green ready light | Ready light off, not red | Single chirps mean attention needed, press the blue i-button. Triple chirps mean a serious fault | Daily, plus a self-test whenever a battery is inserted |
| Philips HeartStart FRx | Blinking green ready light | Ready light off, not red | Single chirps with a flashing i-button point to a self-test error, pads problem, a left-in Infant/Child Key or low battery. Triple chirps mean a serious fault | Daily, plus a battery insertion test |
| Stryker LIFEPAK CR2 | Readiness indicator flashes every 6 seconds | Indicator stops flashing | Alert tone every 15 minutes, which can be disabled in setup | Automatic, with status also reported through LIFELINKcentral |
| Cardiac Science Powerheart G5 | Green Rescue Ready indicator | Red indicator, meaning either a self-test in progress or a detected error | Beeps every 20 seconds while the fault persists | Daily check of battery, pads and electronics. Weekly partial charge. Monthly full energy charge |
| Defibtech Lifeline (DDU-2000 series) | Blinking green when powered off, solid green when on | Blinking or solid red, or no light at all | Two beeps periodically while the indicator flashes red | Power-on, daily, weekly, monthly and quarterly, plus battery insertion |
| HeartSine samaritan PAD | Flashing green every 5 to 10 seconds | Flashing red, or continuous beeping | Continuous beeping. Three rapid beeps can mean the unit is outside its temperature range | Weekly, at midnight GMT every Sunday |
The red that is not a fault
Three situations produce a red indicator on a device that is working correctly. Pulling a unit out of service for any of them wastes time and, worse, trains staff to ignore the indicator.
HeartSine samaritan PAD during its weekly test. The samaritan PAD runs its self-test at midnight GMT every Sunday. The status light blinks red while the test runs and returns to green when it passes. A red flash seen at the wrong moment is not a failure.
Cardiac Science Powerheart during a self-test. On the Powerheart G5 the Rescue Ready indicator turns red both when a self-test is in progress and when an error has been found. The way to tell them apart is the sound: a genuine fault beeps every 20 seconds and persists, a test in progress does not.
Immediately after a battery change. Most units run an insertion self-test as soon as a new battery goes in. Give that test time to complete before reading the indicator.
The rule that resolves all three: a transient red clears on its own within the self-test window. A fault red does not, and on most brands it is paired with a repeating audible alert. If it is still red after the test cycle, treat it as a failure.
The brands where a fault shows as no light at all
This is the failure mode most monthly checks miss, because an unlit indicator reads as “nothing wrong” to anyone walking past.
On the Philips HeartStart OnSite and FRx, ready is a blinking green light and a problem is the light being off. There is no red state. If the light is off and the unit is chirping with the i-button flashing, the cause is a self-test error, a pads problem, a low battery or, on the FRx, an Infant/Child Key left in the device. If the light is off with no chirping and no flashing i-button at all, the likely cause is no battery installed, a fully depleted battery, or a device that needs repair.
On the Stryker LIFEPAK CR2, ready is a readiness indicator that flashes once every 6 seconds. A fault is the indicator simply not flashing, accompanied by an alert tone every 15 minutes. That tone can be switched off in setup, which means a CR2 in a quiet corridor with audio disabled can sit unready and silent indefinitely.
On the Defibtech Lifeline, no light at all is a fault state in its own right and usually means a depleted battery pack.
If your inspection routine says “check the light is green”, it will pass a Philips unit that is completely dead. The check has to be “confirm the indicator is in the ready state for this model”, which is a different instruction.
The ZOLL AED Plus red X
The AED Plus shows its result in a window on the handle: a green check mark means it passed its last self-test and is ready, a red X means it failed and is not ready for use. ZOLL lists the conditions that produce the red X as low or depleted battery capacity, electrode connection problems or missing electrodes, failed ECG circuitry, failed defibrillator charging or discharging circuits, microprocessor or software integrity failures, failed CPR monitoring circuitry, and failed audio circuitry.
Two of those, the battery and the electrodes, are things you can resolve on site. The rest are internal and mean the unit goes back to the manufacturer. The practical sequence is to rule out the two fixable causes first, then stop.
The AED Plus detail most programs get wrong is the schedule. Its self-test runs once every 7 days by default, not daily, though the interval is configurable from 1 to 7 days and software 5.32 and above adds a monthly test. A fault can therefore exist for up to a week before the indicator reflects it, which is the single strongest argument for a physical monthly inspection rather than relying on the window alone.
What to check, in order
Can you use an AED showing a red indicator?
In a cardiac arrest with no alternative device, you use what you have. An AED that has flagged a fault may still deliver a shock, and the alternative is no defibrillation at all. Call emergency services, start CPR and attach the device.
That is an emergency judgement, not a compliance position. A unit showing a fault indicator is not a compliant AED, and in most states Good Samaritan immunity is conditional on the device being maintained as the manufacturer specifies. Leaving a flagged device on the wall is the exposure, not using it in extremis.
Why indicator checks alone fail as a compliance system
The indicator answers one question: did the last self-test pass. It does not tell you that the pads expire in six weeks, that the battery install-by date falls next quarter, or that the two responders trained on that floor both let their certification lapse. None of those will turn the light red until it is already too late to plan around them.
A self-test is a device check. A compliance record is a programme check, and it has to be built from dated inspections, tracked expiry dates for adult and pediatric pads, battery install-by dates, and a current responder list. That is the gap a monthly inspection closes.
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About the Author
Kyle Nowack
Founder, AED Log
Kyle Nowack founded AED Log in 2019 to help organizations simplify AED program management. His work focuses on software that tracks AED devices, pad and battery expiration dates, inspection records, and user certifications, helping schools, fitness centers, businesses, and public facilities stay on top of AED readiness.
Through the AED Log blog, Kyle shares practical guidance on device tracking, maintenance planning, and program documentation to help organizations manage their AED responsibilities with greater confidence.