How to Install a Bilge Pump Alarm on Your Boat

A bilge pump alarm may help save your sailboat - as well as you if you're aboard offshore.

Most boats large enough to have an inboard engine also have through-hulls and other means by which water can enter the boat. In event of a failure in any of these systems, or a problem in the integrity of the hull, water can overwhelm an automatic bilge pump and, in extreme cases, sink the boat. It can be difficult to find and correct a leak once the water becomes deep enough to obscure visibility in all areas.

To guard against the problems of leaks, consider installing a bilge pump counter, bilge alarm, and/or bilge high water alarm. These three systems work in different ways and offer different benefits, and you may want to use more than one. This article describes the use of a bilge alarm.

Start with an Automatic Bilge Pump

Every boat gains from an automatic bilge pump that comes on when an internal or external float switch or sensor indicates water has risen to a certain level in the bilge. On many boats the bilge pump is wired into the electrical control panel, tempting the owner to shut it off when leaving the boat or at other times - defeating the whole purpose of being an automatic pump. Or even if the switch is left on, the power to it may be cut if you shut the main battery switch off when leaving the boat, as generally should be done to prevent losing power to a short or other systems left running.

A simple solution is to wire the automatic bilge pump directly to one of the boat's batteries with an inline fuse. No matter what is done with the panel or battery switch, the pump will run as long as the battery has power. The only downside is that the pump may get stuck on and drain the battery completely (and/or overheat the pump). If you have multiple batteries the risk is minimal if you shut off the battery switch so that they are not connected in parallel to the pump. The risk is preferred to potential damage from a leak when you're away from the boat.

Why Use a Bilge Alarm?

Because the bilge pump often cannot be heard over the sound of the boat's engine or ​the wind and waves, a bilge alarm informs you when the pump is running, or running too long. With a small leak, you might hear the pump come on and run for a minute or two, then shut off - but start again soon, alerting you to the situation so that you can track down and fix the leak before it becomes a bigger problem. With a larger leak, such as a busted hose at a through-hull fitting or a breach of the hull, you may hear the alarm come on and not go off soon as you'd expect. If the alarm is still sounding after a couple minutes, water may be coming in faster than the pump can handle it, and you better move quickly if you are to save the boat.

Types of Bilge Alarms

As with most marine electronics, you can go simple and cheap or complex and more expensive. At the low end, a do-it-yourselfer can buy an inexpensive loud 12-volt alarm at Radio Shack and wire it directly into the bilge pump system so that each time the float switch turns on, power goes to both the pump and the alarm. You'll hear the alarm every time the pump runs, including the pumping of "normal" water from the stuffing box, condensation and rainwater ingress, etc., but to many, that's preferable to the thought of water coming in an emergency and not being aware of the pumping.

Many digital marine bilge alarms have a mute function switch that allows you to temporarily shut off the alarm. You could, for example, quietly pump the bilge dry before going to sleep at anchor so that rolling motion in the night setting off the float switch to pump out normal water accumulation doesn't blast you awake in the middle of the night. Expect to pay $60 to $70 for an average marine system.

At the high end, alarm units are available with more advanced functions such as to set off the alarm only after 2 minutes of continuous pumping. This allows silent pump operation for most routine pumping of normal accumulations while alerting you to a potential leak signaled by prolonged pumping.

Alternatively, some boaters prefer to use a high water alarm rather than a bilge pump alarm. Learn more about that type here.


Installation of these alarms is relatively simple, and the wiring can often run alongside the bilge pump wires. Follow the instructions for the model you choose, remembering to locate the alarm itself in a place where it can be heard both inside and outside the cabin.

If you are building your own system, you need only a 12-volt alarm and the appropriate wire. Like the bilge pump, it is better to wire the alarm directly to a battery (use an inline fuse) rather than through the electrical panel. Route the alarm wire so that when the float switch completes the circuit to provide power to the pump, it also provides power to the alarm.

Where to Buy

  • Water Witch (high-end marine electronics, a variety of systems)
  • Aqualarm (several models)
  • Defender Marine (multiple products, discount prices)