Table of Contents
Overview
The Shelly 1PM is one of the most popular smart relays in the Home Assistant community — and for good reason. It's a compact, Wi-Fi-connected relay that fits inside a standard electrical switch box, allowing you to make any ordinary light switch or electrical device smart without replacing the switch or outlet. The PM suffix means it includes power monitoring — measuring real-time power consumption of whatever it controls.
For Home Assistant users, the Shelly 1PM is close to ideal: local API, MQTT support, no cloud requirement, and a native Home Assistant integration that works out of the box. If you care about local control and hate cloud-dependent devices, Shelly products should be on your radar.
Shelly 1PM Smart Relay
Single-channel 16A smart relay with power monitoring. Fits in standard back boxes. Wi-Fi with local API and MQTT. Compatible with Home Assistant, Alexa, and Google Home.
Check Price on AmazonHardware & Dimensions
The Shelly 1PM is tiny — measuring just 39mm × 36mm × 17mm. This is by design: it needs to fit inside the back box of a light switch or outlet, alongside the existing wiring. In practice, it fits comfortably in most UK-standard back boxes, though very shallow boxes may require a deeper replacement.
The relay supports up to 16A continuous load — enough for most lighting circuits and many appliance applications. It supports both live-only and neutral-required wiring configurations, though power monitoring accuracy is better with neutral wire access.
There's a physical button on the device itself for manual control (useful during setup or as a physical override), and a status LED. The device gets warm under load — this is normal — but it includes thermal protection that automatically cuts the load if temperatures exceed safe thresholds.
Shelly designed the 1PM for 110–240V AC mains, making it suitable for both US and European electrical systems.
Setup & Configuration
Initial setup is done via the Shelly app (iOS/Android) or directly through the device's built-in Wi-Fi access point. On first power-up, the Shelly 1PM creates its own Wi-Fi network (ShellyXXXXXX). You connect to this network from your phone, open the configuration page, and set your home Wi-Fi credentials. The device then joins your network and is discoverable.
The Shelly web interface is accessible via your browser at the device's local IP address — no app required. From here you can configure input/output modes, set timers, configure MQTT, enable CoAP (for Home Assistant local discovery), and view power usage history. It's a clean, functional interface that works well on both desktop and mobile browsers.
For the most common use case — smart light switch — wiring involves connecting the Shelly between the live supply and the switch. Shelly provides clear wiring diagrams for all common configurations on their website, covering single-wire (no neutral), two-wire (with neutral), and two-way switching setups.
Home Assistant Integration
Home Assistant integration is where the Shelly 1PM truly shines. The official Shelly integration in Home Assistant auto-discovers all Shelly devices on your local network via CoAP — no configuration required. Once discovered, the Shelly 1PM appears as:
- A switch entity (on/off control)
- A power sensor (real-time watts)
- An energy sensor (cumulative kWh, compatible with the Energy Dashboard)
- Voltage and current sensors
- Device temperature sensor
All of these update in real time with sub-second latency. The Energy Dashboard integration means you can track exactly how much electricity each Shelly-controlled circuit uses — lighting, appliances, heating elements — and build energy-aware automations. For example: turn off a circuit if it's been consuming standby power for more than 2 hours.
Automations work exactly as you'd expect in Home Assistant. You can trigger on power consumption thresholds ("send a notification if the washing machine has finished"), create time-based schedules, integrate with presence detection, and more. The Shelly 1PM is a workhorse device that enables some of the most practically useful Home Assistant automations.
Power Monitoring
The power monitoring in the Shelly 1PM is accurate to within approximately 1–2% of measured loads in our testing. For a device costing under $20, this is remarkably good. We tested it against a calibrated power meter across various loads: LED lighting (15W–120W), an electric kettle (2000W), and a refrigerator compressor motor — accuracy was consistent across all load types.
Historical power data is stored on the device and can be pulled via the local API or MQTT. Home Assistant's Energy Dashboard aggregates this into daily and monthly usage graphs, making it easy to see where your electricity is going. Users with multiple Shelly 1PM devices across their home can build a detailed whole-home energy map.
Local Control & MQTT
Unlike the majority of smart home devices that require cloud connectivity, the Shelly 1PM operates entirely locally. Commands sent via the local REST API or MQTT respond in under 50ms — far faster than any cloud-dependent device. Your automations continue to function even if your internet connection is down.
MQTT configuration is straightforward: enter your MQTT broker's IP address and credentials in the Shelly web interface, and the device immediately starts publishing state changes and accepting command topics. This makes Shelly devices natural citizens of any MQTT-based smart home setup.
Shelly Cloud is available as an optional add-on for remote access outside your home network, but it's entirely optional. Many advanced users never enable it, relying instead on VPN access to their home network for remote control.
Tasmota and ESPHome firmware can be flashed onto older Shelly 1PM models (which use ESP8266 chips) for even more customisation. Newer Gen 2 hardware uses different chips and can't be re-flashed as easily, though Shelly's native firmware is good enough for most use cases.
Verdict
Our Verdict: 5/5 — Essential for Home Assistant Users
The Shelly 1PM is one of the most practical and capable smart home devices available at any price point. For Home Assistant users especially, it's close to essential: local control, power monitoring, native HA integration, MQTT support, and a compact form factor that fits where smart plugs and smart switches can't go.
At under $20, it's also exceptional value. The only caveat is that installation requires electrical work — but for anyone comfortable with that, the Shelly 1PM is one of the best investments you can make in your smart home.
Buy if: You want to smartify existing light switches or control circuits with power monitoring, and you use Home Assistant or any MQTT-compatible platform.
Skip if: You need something plug-and-play with zero wiring — go for a smart plug instead.
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