Shelly 1 vs 1PM vs 2PM: which one do you need?

The Shelly 1, Shelly 1PM and Shelly 2PM are small smart modules. An electrician fits one behind an existing light switch or powerpoint, and whatever that switch controls becomes smart: you can turn it on and off from your phone, by voice or on a schedule. The switch on the wall keeps working as normal.

The three look almost the same, and the names hint at the difference. PM stands for power metering, which means it shows how much power something uses. The 2 means it controls two things instead of one.

This guide covers the Gen4 versions we stock. If you want to see the whole Shelly range sorted by job instead, Which Shelly do I need? walks you through it.

The three side by side

Shelly 1: the simplest, and the one for garage doors

The Shelly 1 works like a plain on/off switch. What makes it different is that it doesn't send any power out of its own. It just connects two wires together, the way pressing a button does.

That's why it's the one to use for a garage door or gate. Your electrician connects it to the same spot as the opener's wall button, so tapping your phone does exactly what pressing that button does. Check your opener's manual first, because a few models don't have a simple button connection.

It works for lights too. Your electrician adds one short extra wire so power can pass through it to the light.

What it can't do is tell you how much power something uses. It knows whether a light is on or off, and that's all.

Shelly 1PM: one light or appliance, with power monitoring

The Shelly 1PM turns one light or appliance on and off, and it can handle the same load as the Shelly 1. It also measures how much power flows through it, which opens up some handy tricks:

• See what a heater costs to run.
• Get a notification when the washing machine has finished.
• Find out a light globe has blown, because it has stopped drawing power.

It also switches itself off if the power supply misbehaves or it gets too hot, and the 2PM does the same. The Shelly 1 only switches off if it overheats.

The 1PM does send mains power out to whatever it controls, so it can't work a garage door opener's button.

Shelly 2PM: two things at once, or a motorised blind

The Shelly 2PM is two switches in one unit, and each shows its own power use. It suits a double light switch, such as a bathroom with the light on one switch and the exhaust fan on the other. It costs less than two 1PMs.

Each side handles up to about 2,400 watts, which covers lights, fans and small appliances but not a large heater. Check what a Shelly can switch if you're not sure.

The 2PM can also run a motorised roller blind, roller shutter, venetian blind or awning, raising and lowering it from your phone or on a schedule. Shelly recommends motors with built-in stop points, set up before the Shelly goes in, so the motor knows where to stop. It can also stop the blind if something gets in the way.

Which one for which job

Whichever you choose, your wall switch keeps working. In the Shelly app you can set it to work as a normal on/off switch or a push button, or have it trigger something else entirely.

What about the Plus and Gen3 versions?

You'll still see names like Shelly Plus 1 and Shelly Plus 2PM in older guides and forums. Plus was an earlier generation, since replaced by Gen3 and then Gen4. Each one still does the same job.

We also stock the Gen3 versions, and they cost less. The main difference is how they connect. Gen4 works with Apple Home straight out of the box, and can connect to a Zigbee hub instead of Wi-Fi if you already have one. With Gen3, Apple Home support depends on the model. Shelly generations compared covers the rest.

When you book one, show them our Shelly wiring diagrams for the model you've picked.