What a freeze alarm actually does at a cottage

A freeze alarm watches the temperature inside the cottage and tells you when it drops below a level you set. That is the whole job. It does not stop a pipe bursting. It tells you the building is at four degrees on a Tuesday in January while there is still time to phone someone who lives nearby.

That distinction matters, because the marketing around these things tends to promise prevention, and prevention is not what a sensor does.

What it is really protecting you from

Almost nobody loses a cottage to one dramatic cold snap. They lose it to a furnace that quit on the 3rd of January and was not discovered until the 20th. By then the damage is not a pipe, it is the ceiling below the pipe, the floor below that, and the mould behind everything.

The gap between the failure and the discovery is the entire problem. A freeze alarm closes it from two weeks to twenty minutes.

What it needs to work

Three things, and if any one of them is missing you have bought a thermometer.

• Power. It has to run through the outage that probably caused the cold in

the first place. That means either a battery-backed sensor or a hub on a small UPS.

• A way to reach you. WiFi is fine when the internet is up, but a power cut

takes the modem with it. For a cottage that sits empty for long stretches, a cellular path is the honest answer.

• Somewhere sensible to sit. The coldest room, not the warmest. Usually

that is a crawlspace, a pump room or the far end of a wing over an unheated space.

Where people put them wrong

The most common mistake is one sensor in the main room. The main room is the last place in the building to get cold. By the time it reads five degrees, the crawlspace has been below freezing for two days.

The second is setting the threshold too low. Four or five degrees gives you hours of margin. Setting it at one degree means you find out at the same time the plumbing does.

What it does not do

It will not help if nobody can get there. A freeze alarm is only as good as the person forty minutes away who has a key and will go and look. Before you buy sensors, work out who that person is. Sometimes that conversation is the whole solution and the hardware is a detail.

It also will not tell you a pipe has already burst. That is a different sensor sitting on the floor, and at a cottage you usually want both.

The version that is worth doing

Temperature in the two or three coldest spots, a leak sensor at the water heater and under the kitchen sink, a hub that keeps working when the internet does not, and a thermostat you can turn up from the car so the place is warm when you arrive. Everything in that list survives a power cut and reaches your phone.

That is not an expensive build. It is the one we install most often, and it is usually the reason people call us in the first place.