How do I get a phone alert when my walk-in warms up?

What you need

Three things: a sensor in each box, something that sends the alert when a limit is crossed, and a connection that does not depend on the store being open. That is the whole system.

How to stop false alarms

Every freezer warms up during defrost, and every cooler warms up when a delivery is being put away. An alarm that fires the moment a limit is crossed will wake you up for nothing, and within a month you will ignore it.

Set a delay. For example, alert when the freezer has been above 5°F for 20 minutes. A defrost comes and goes inside the delay. A dead compressor does not.

Small sensors or a panel?

• One or two boxes with good Wi-Fi: a stand-alone Wi-Fi sensor in each is the cheapest way to start. You will replace batteries, and it goes quiet if the internet or power drops.
• Several boxes, or product you cannot afford to lose: a wired panel reads every sensor, keeps running on a battery in an outage, sends alerts over its own cellular connection, and shows all the boxes on one screen.

Keep the history

A stored log of every reading is useful beyond the alarm. It shows a box that is slowly getting worse before it fails, and it gives you something to hand an inspector or an insurance adjuster. Ask your own inspector what records they accept.

Who should get the alert

Send it to more than one person. The owner, a manager, and your refrigeration contractor if they agree to it. An alert that reaches one phone on silent is no alert.