Sump pump alarm
A sump pump alarm tells you when the water level in your pit is rising faster than the pump can remove it — or when the pump has stopped altogether. The best ones also alert you remotely, even during a power outage.
A sump pump alarm uses a float or reed switch set above the normal pump level and sounds a horn (typically 85–87 dB) plus a visual indicator when water rises too high. Standalone models include a 9V or AA battery so they keep working during a power outage.[1][2] Wi-Fi-connected models from Liberty and Zoeller push notifications to your phone at no monthly cost.[3][2]
What a sump pump alarm does
The alarm monitors water level independently from the pump. When water rises above the sensor's trigger point — which sits above the pump's normal on-level — it sounds a horn, lights an indicator, and (on Wi-Fi models) sends a phone notification. Zoeller states in its technical data that high-water alarms should be installed on every system, large or small, because "a high water alarm can save the headache and stress of cleaning up a catastrophe after the fact."[2]
Integrated alarms inside battery backup pump systems also monitor pump health: whether the pump ran, whether AC power is present, battery state, and — on advanced models — temperature. Standalone alarms detect only water level, but they work with any pump brand and are easy to add to an existing setup.
Types of sump pump alarms
Standalone alarms
These mount on the wall near the pit and include their own float or reed sensor. They operate independently from the pump and can be added to any sump pit regardless of pump brand.
Standalone alarm comparison
| Alarm series | Sensor type | Sound | Enclosure | Battery backup | Wi-Fi | Source |
|---|---|---|---|---|---|---|
| Liberty ALM-P1 / ALM-2 Standard models | Snap-on float (ALM-P1) or tethered float (ALM-2) | 86 dB | NEMA 1, indoor only | 9V battery | None | [1] |
| Liberty ALM-P1-EYE / ALM-2-EYE NightEye Wi-Fi models | Same as standard, plus NightEye wireless module | 86 dB | NEMA 1, indoor only | 9V battery | Built-in (NightEye) | [1] |
| Zoeller APak 10-4012 Indoor, tethered float | 15 ft tethered float switch, 6 ft power cord | 87 dB | NEMA 1, indoor only | 2× AA batteries | None | [2] |
| Zoeller APak 10-4011 Indoor, reed sensor | 15 ft reed sensor, 6 ft power cord | 87 dB | NEMA 1, indoor only | 2× AA batteries | None | [2] |
| Zoeller APak 91104-0001 Outdoor/indoor | 15 ft tethered float switch; field-wired power | 85 dB | NEMA 4X, indoor or outdoor | None | None | [2] |
| Zoeller Z Control 10-4013 / 10-4014 Z Control Wi-Fi indoor alarms | Reed sensor (10-4013) or mechanical float (10-4014) | 87 dB | NEMA 1, indoor only | 2× AA batteries | Built-in (Z Control) | [2] |
Alarms built into battery backup systems
Every battery backup sump pump system includes some form of alarm. Integrated alarms go further than standalone units — they monitor the pump, the charger, and the battery, not just water level.
Built-in alarm features by backup system
| System | Conditions monitored | Battery backup (alarm) | Wi-Fi / remote alert | Self-test | Source |
|---|---|---|---|---|---|
| Liberty 442-10A / 442-25A Standard models | High water, AC power loss, low battery, alarm test | 9V — 72 h standby | None | Manual test button | [3] |
| Liberty 442-10A-EYE / 442-25A-EYE NightEye Wi-Fi models | Pump activation, high water, AC power lost, Wi-Fi lost, fuse/DC pump fault, battery charge, critically low battery, basement temperature | 9V — 12 h active, 7 d standby | NightEye (built-in); no subscription | Manual test button; remote test via app | [3] |
| Zoeller Aquanot Fit 508 Z Control built-in | Connection fault, power outage/restored, pump activation, pump cycled, high water, battery fault, switch fault, pump fault | Not specified in documents reviewed | Z Control (built-in); no monthly cost | Automated self-test; manual test button | [4] |
| Basement Watchdog Big Dog CONNECT BWD12-120C | Battery, battery fluid level, power, pump conditions | Not specified in documents reviewed | BW-WiFi module (sold separately); no subscription | Weekly automated pump test | [5] |
| Wayne ESP25-N | AC power loss (30-second tone), pump start (3-second tone), low battery (chirp) | No separate alarm battery; pump battery powers system | None | Manual float-lift test | [6] |
What each alert tells you
High water. The water level has risen above the alarm sensor — above the pump's normal on-level. The primary pump has failed, lost power, or cannot remove water as fast as it's coming in. Cut power to the pump, inspect the float switch, and check the circuit breaker. If the pump is running, water inflow may exceed its capacity.
Power loss. AC power to the system has been interrupted. On the Wayne ESP25-N, a 30-second tone sounds and the power-failure light illuminates; the system resets automatically when power returns.[6] On battery backup systems with NightEye or Z Control, a phone notification arrives within seconds, which is especially useful when you're away from home.
Pump run / pump activation. Available on systems with integrated monitoring (Liberty NightEye, Zoeller Z Control). The backup pump has started — usually because the main pump failed or power is out. Useful for confirming the backup is working when you're not home.
Battery / low battery. On standalone alarms, a chirp about twice per minute means the 9V or AA backup battery needs replacement.[1] On integrated systems, the controller monitors the deep-cycle pump battery: a red indicator or audible alert means the battery cannot reliably power the pump. Replace the battery before the next outage.
Power source during an outage
Power outages and pump failures often happen together — the pump trips a breaker, or a storm cuts power and floods the pit simultaneously. That's why the alarm needs its own backup power separate from the pump.
Standalone Liberty ALM and Zoeller APak alarms both require a 9V or AA battery installed at all times. Liberty specifies a 9V battery must be installed in the device at all times to ensure proper operation, and recommends replacing it every 12 months or when the low-battery indicator lights.[1] Both Liberty and Zoeller recommend connecting the alarm to a circuit that is separate from the pump — if the pump trips its breaker, the alarm stays powered.[1][2]
On integrated systems, the Liberty 442's controller uses a 9V battery: up to 72 hours standby on standard models, or 12 hours in active alarm mode and 7 days in standby on NightEye models.[3] Wi-Fi notifications continue for as long as your home router has power (consider putting the router on a UPS during outages).
Where to mount the sensor
The alarm sensor must sit above the primary pump's normal on-level, not at the same height. If set at the same level, the alarm would sound on every normal pump cycle. Liberty Pumps states that the snap-on sensor's activation point should be slightly higher than the pump activation point.[1] Zoeller's installation diagram for APak alarms shows the alarm float above the pump ON level.[2]
For the alarm enclosure itself, Liberty recommends mounting it 48–66 inches above floor level, so it's audible and the visual beacon is easy to see.[1]
Follow the manufacturer's instructions for your specific model — float cord length and sensor type differ between sump (snap-on enclosed float, ALM-P1) and sewage (tethered float, ALM-2) configurations.
Why is my sump pump alarm going off?
The three most likely causes:
- High water — pump problem. The pit water has risen above the alarm sensor. Check that the primary pump is plugged in and its float switch isn't stuck. Inspect the circuit breaker. A pump that hums but won't run may have a failed impeller or a locked motor.
- High water — inflow exceeds pump capacity. The pump is running but can't keep up during a heavy storm. A battery backup pump or water-powered backup can provide extra capacity. See the sump pump battery backup guide for options, or the water-powered backup page for no-power alternatives.
- Low backup battery. A chirping alarm rather than a sustained horn usually means the 9V or AA alarm battery is low — not that the pit is flooding. Replace it promptly so the alarm is ready for an actual event. Liberty's ALM series chirps about twice per minute when the 9V battery needs replacement.[1]
After fixing the root cause, reset the alarm: the Liberty ALM audible alarm can be silenced with the Silence button and stays silenced for 6 hours, then resets automatically when the water level drops.[1] On Zoeller APak alarms, press Silence to mute and hold for 3 seconds to reset.[2]
Testing the alarm
Liberty Pumps recommends testing the ALM-series alarm every 6 months.[1] Testing methods by sensor type:
- Snap-on enclosed float (ALM-P1): Raise the water level in the pit above the float's activation mark. Alternatively, hold a cup of water near the sensor to confirm float operation.
- Tethered float (ALM-2): Manually tip the float upward; the alarm should sound. Return the float to its resting position to reset.[1]
- Zoeller APak: Press the Test button or — on Z Control models — initiate a test remotely via the Z Control app.[2]
- Liberty 442 / Wayne ESP25-N: Use the alarm test button on the controller, or unplug the main pump and lift the float switch to verify the backup and alarm respond.[3][6]
- Basement Watchdog Big Dog CONNECT: The system runs a weekly automated pump test; you can also check the controller display.[5]
Related pages
- Sump pump battery backup — compare systems
- Battery backup installation guide
- Sump pump battery: types and replacement
- Water-powered sump pump backup
- Basement Watchdog backup sump pumps
- Zoeller backup sump pumps
- Wayne backup sump pumps
Frequently asked questions
- Why is my sump pump alarm going off?
- The most common cause is water rising above the alarm sensor — meaning the primary pump has stopped, lost power, or cannot keep up with inflow. Check that the primary pump is plugged in, its float switch moves freely, and the breaker has not tripped. If the pump is running but the pit level keeps rising, inflow exceeds pump capacity. A separate low-battery alarm (chirp or flashing LED) means the 9V or AA backup cell in the alarm needs replacement, not that there is a water problem.
- Do sump pump alarms work when the power is out?
- Yes, if they have battery backup. Standalone Liberty ALM-series alarms carry a 9V backup battery that keeps the high-water sensor active when AC power fails. Standalone Zoeller APak alarms use two AA batteries for the same purpose. The Liberty 442 backup-system control panel uses a 9V battery that runs the alarm for up to 72 hours in standby, or 12 hours in active alarm mode on NightEye models.
- Where should the alarm sensor sit in the sump pit?
- Place the sensor's activation point slightly above the primary pump's normal on-level so it only sounds when the water is higher than the pump would normally allow. Liberty Pumps states this directly in the ALM installation manual. Both Liberty and Zoeller installation diagrams show the alarm float positioned above the pump's on-level. Connect the alarm to a circuit separate from the pump so a tripped breaker does not knock out both.
- Can I add Wi-Fi alerts without replacing my backup pump system?
- Yes. Zoeller's Z Control APak alarms (10-4013 with reed sensor, 10-4014 with mechanical float) are standalone Wi-Fi alarms that work with any pump brand. Liberty's ALM-EYE models (ALM-P1-EYE, ALM-2-EYE) are standalone Wi-Fi alarms. The Basement Watchdog BW-WiFi module is sold separately and adds app notifications to any Basement Watchdog CONNECT-equipped backup system.
- What is the difference between a high-water alarm and a power-loss alert?
- A high-water alarm detects rising water directly with a float or reed sensor set above the pump's normal operating level. A power-loss alert (available on systems like the Liberty 442 NightEye and Zoeller Aquanot Fit with Z Control) notifies you when AC power is interrupted, before water can rise. Systems with both give you earlier warning.
- How often should I test my sump pump alarm?
- Liberty Pumps recommends testing the ALM-series alarm every 6 months: raise the water level above the sensor or, for tethered-float models, tip the float manually. The Liberty 442 and Zoeller Aquanot systems have test buttons on the controller. Basement Watchdog Big Dog systems run a weekly automated self-test of the pump.
Sources
- ALM-Series Indoor Alarms Installation and User Manual (2138000C) — Liberty Pumps, document dated 2016. Accessed 2026-11-03. Manufacturer install manual hosted by a retailer (Septic Solutions). Covers models ALM-P1, ALM-2, ALM-2-1, SJ10A and NightEye -EYE variants.
- APak Alarm Systems Technical Data Sheet (FM0732) — Zoeller Co., document dated 2026-07. Accessed 2026-11-03. Revision 0726; supersedes 0922.
- 442-Series Battery Back-Up Pumps brochure (LLIT006746-R07/23) — Liberty Pumps, document dated 2023-07. Accessed 2026-11-03. Manufacturer brochure hosted by a retailer.
- Battery Backup Systems sales sheet (FM3525) — Zoeller Co., document dated 2024-12. Accessed 2026-11-03.
- Big Dog CONNECT battery backup sump pump brochure (BWD12-120C) — Basement Watchdog, document dated 2018-06. Accessed 2026-11-03. Manufacturer brochure hosted by Home Depot.
- ESP25-N Operating Instructions and Parts Manual (600001-001 B) — WAYNE / Scott Fetzer Company, document dated 2018-08. Accessed 2026-11-03. Manufacturer manual hosted by Home Depot.