Shelly i4 Gen3 Review: A 4-Input Trigger That Turns Any Switch Into a Smart Automation
No relay outputs of its own, just four wireless inputs that reliably trigger scenes, other Shelly relays and Home Assistant automations.
The Shelly i4 Gen3 is not a load-switching relay, it is a 4-channel input device that turns existing switches, sensors or momentary buttons into triggers for scenes, automations, or other Shelly relays over Wi-Fi. Buyers use it for everything from beam-break sensors and smoke alarms to triggering garage door relays and toggling other Shelly-powered circuits through Home Assistant. It is well suited to tinkerers already in the Shelly or Home Assistant ecosystem, but some less technical buyers found the scene and automation setup harder to grasp than a typical smart switch.
- Home Assistant and smart-home tinkerers
- Triggering other Shelly relays or scenes
- Adding smart automation to existing switches and sensors
- DIY sensor and alarm integrations
Pros
- Four flexible digital inputs for switches, sensors and buttons
- Reliable, fast response for triggering scenes and automations
- Smooth Home Assistant and Alexa integration
- Works as a Bluetooth gateway
- Compact enough to embed behind existing wall switches
Cons
- No relay outputs or dry contacts of its own, input only
- Scene and automation setup can be tricky for non-technical users
- No Zigbee, Z-Wave, Thread or 5GHz Wi-Fi
- Free Alexa routines limited to 3 scene triggers
Who is the Shelly i4 Gen3 for?
The i4 Gen3 has four digital inputs and no relay outputs of its own, so it is built for buyers who already have a switch, sensor, or momentary button and want to turn its state changes into a smart trigger. Reviewers use it to wire in beam-break sensors, smoke and fire alarms, 3D printer components, and laser cutter outputs, feeding all of it into Home Assistant for logging and automation. It is also a popular way to keep a physical rocker switch working alongside voice control, wiring the switch into the i4 to toggle a separate Shelly relay (for example, a garage door opener or a Shelly Pro 4PM) rather than switching load directly.
What buyers love
The dominant theme is reliability paired with flexibility for automation-minded buyers: multiple reviewers describe it as fast and instantly responsive when detecting input changes, whether from a beam-break sensor, alarm contact, or physical switch. It integrates smoothly with Home Assistant, which several buyers specifically praise for making complex projects (3D printer monitoring, laser cutter tracking, multi-switch lighting control) straightforward. Its compatibility with Alexa scene triggers and its Bluetooth gateway function add versatility, and buyers note it keeps working well after being embedded behind existing wall plates or momentary switches for months.
What to know before you buy
The i4 Gen3 has zero relay channels and no dry contacts of its own. It is strictly an input/trigger device, and a few buyers who expected a switch or relay were confused or disappointed. Setup and scene programming can be a hurdle for less technical users, with a couple of reviews describing the configuration as difficult without outside help or YouTube tutorials. It also lacks Zigbee, Z-Wave, Thread and 5GHz Wi-Fi, working over 2.4GHz Wi-Fi and Bluetooth only, and its Alexa routines are capped at 3 free scene triggers before requiring a paid tier. There is no DIN rail mount or physical on/off button, and safety-protection specs (overcurrent, overvoltage) are not documented for this input-only device.
Is the Shelly i4 Gen3 worth it?
For its specific job, converting any switch or sensor contact into a Wi-Fi automation trigger, the i4 Gen3 delivers consistently, with buyers reporting fast, dependable performance across a wide range of DIY projects. It is a niche but valuable piece for Home Assistant and Shelly-ecosystem users building multi-device automations, though newcomers expecting a simple smart switch replacement should understand upfront that it switches nothing itself, it only triggers other devices.
Frequently asked questions
Does the Shelly i4 Gen3 switch power on its own?
No. It has zero relay channels and no dry contacts of its own, it is strictly a 4-input trigger device used to feed switch or sensor states into automations or to control other relays.
Can the Shelly i4 Gen3 trigger other Shelly devices?
Yes, a common use case is wiring an existing physical switch into the i4 Gen3 to toggle a separate Shelly relay, such as one controlling a garage door or a lighting circuit.
Does the Shelly i4 Gen3 work with Home Assistant?
Yes, it integrates directly with Home Assistant, and buyers frequently use it for automation projects like sensor monitoring, alarm triggers and multi-switch lighting logging.
Does the Shelly i4 Gen3 support Zigbee or Z-Wave?
No. It connects over 2.4GHz Wi-Fi and Bluetooth only, with no Zigbee, Z-Wave, Thread or 5GHz Wi-Fi support.
Is the Shelly i4 Gen3 hard to set up?
Basic wiring is straightforward, but configuring scenes and automations can be more involved than a simple smart switch, and a few buyers needed outside tutorials to get advanced setups working.
