Shelly 1 Gen3 vs Shelly i4 Gen3

The Shelly 1 Gen3 wins overall because it can actually switch a load. It has a relay with dry and wet contact modes, works on AC or DC, and adds Apple HomeKit and SmartThings to its integration list. The Shelly i4 Gen3 is cheaper and marginally better rated, but it is input only.

Outputs. The Shelly 1 Gen3 has one relay channel and can close or open a circuit, including isolated dry contacts for gates and boilers. The Shelly i4 Gen3 has zero relay channels and four inputs instead, so it reads switch presses and triggers automations elsewhere in your system.

Only indirectly. It has no relay, so it cannot switch a circuit itself, but its four inputs can trigger scenes or automations that control other devices, including a Shelly 1 Gen3 elsewhere in the house. That combination is common: the i4 handles the wall switches, a relay module does the switching.

Yes, on mains power. The Shelly 1 Gen3 needs a neutral on 110-240V AC and runs without one only from a 12-48V DC supply. The Shelly i4 Gen3 is powered from 110-240V AC through its L and N terminals, so it needs a neutral too, even though it only monitors inputs rather than powering a load.

Buy the Shelly 1 Gen3 to make an existing circuit smart: a light, a garage door, a sprinkler valve or a boiler. Its 16A rating, dry and wet contact modes, AC or DC power, Matter support and HomeKit compatibility cover almost any project, and it fits behind a switch or in a junction box.

Buy the Shelly i4 Gen3 if you want to keep your existing wall switches and buttons but use them to trigger smart scenes. Its four inputs are fast and reliable, it works as a Bluetooth gateway, and it hides behind a switch plate, but remember it cannot switch a load on its own.