Alert your phone about a water tank level with a float switch and the Shelly Plus Uni

We get this question a lot: «I have a clean-contact water level float switch and I want Shelly to alert my phone when the tank is empty or full. I tried a Shelly 1 and it didn't give me the option to send messages. Does the Shelly Plus Uni work by connecting the float's two wires?». The short answer is yes — the Plus Uni is exactly the device for this. Here's how, with the details worth knowing before you buy.

How the float connects to the Plus Uni

The Shelly Plus Uni is a module built to read sensors. It has two digital inputs that take a potential-free contact (a dry contact) directly — which is exactly what a level float switch is. You connect the float's two wires to a digital input and that's it: the module detects whether the contact is open or closed and alerts your phone when it changes.

Shelly explicitly lists it as compatible with float, reed, moisture and motion sensors, so your case is textbook.

There's an important difference from a Shelly 1, and it's what explains why that one «didn't give you the option»: the Plus Uni is low-voltage. It doesn't plug into 230 V; it runs on 9-28 V DC (also 8-24 V AC or 5 V DC), so it needs a small power supply and mounts inside an enclosure or the equipment itself.

One float alerts one level; for empty and full, two

This nuance matters so you're not caught out. A contact float gives a single level: it changes state when the water crosses the point where you place it. With one float you'll get one alert (say «tank empty» or «tank full»), not both.

If you want to be alerted for both empty and full, you need two floats: one at the top (full level) and one at the bottom (empty level). And this is where the Plus Uni fits perfectly: with its 2 digital inputs, you connect one float to each input and tell the two states apart with a single module.

How you get the phone alert

Nothing exotic to program; it's done in the Shelly app:

1. Add the Plus Uni in the app (pair over Bluetooth), connect it to your Wi-Fi and enable the digital input in its menu.
2. Create an action on that input: when it changes state (the float triggers), have it fire a notification.
3. Get the alert wherever you are: with the device online, the notification reaches your phone even when you're not home.

This is exactly the use Shelly documents for the Plus Uni (tank-level monitoring, for example in campers, with a phone alert). And if you use Home Assistant, you can handle it locally too.

What you need and what to buy

The checklist so it works first time:

• The module: Shelly Plus Uni, with its 2 digital inputs and phone notifications. The recommended pick for this.
• The power supply: a 9-28 V DC supply (a small 12 V adapter is more than enough). Remember: the Plus Uni does not plug into 230 V. If you don't have one, tell us and we'll recommend the right one.
• The float: one per level you want to watch (one for a single alert, two for empty and full).

Is there another one that does the same job? Yes: if you want more inputs, the Shelly Plus i4 DC reads up to 4 potential-free contacts, also on low-voltage DC, and works just as well for floats with phone alerts. For one or two floats, the Plus Uni is more complete (it also has an analog input, in case one day you want a continuous-level probe).

Why the Shelly 1 Gen3 didn't do it

You didn't do anything wrong. The Shelly 1 is a relay meant to switch a load (turn something on at 230 V), and its input is designed to drive that relay, not to read a sensor and notify you. The Plus Uni is the opposite: a low-voltage module built to read sensors (floats, reed, probes) and fire actions and notifications. It's the right tool for what you want.

FAQ

Does it work just by connecting the float's two wires?

Yes. The float is a potential-free contact; its two wires go to a digital input on the Plus Uni. It carries no voltage of its own — the module reads it.

Will it alert me even when I'm not home?

Yes, as long as the Plus Uni is connected to your Wi-Fi and the internet. The notification reaches your phone via the Shelly cloud.

Can I track empty and full at the same time?

Yes, with two floats (one per level) on the Plus Uni's two digital inputs. With a single float you'll get one alert.

How is it powered?

Low voltage: 9-28 V DC, 8-24 V AC or 5 V DC. It doesn't connect directly to 230 V; it needs a small supply.

Can it also switch something, like a pump?

Yes. The Plus Uni has two dry-contact outputs that can drive, for example, a pump's relay based on the level. Note: these are low-current outputs for piloting, not for powering the pump directly.

What if I want the exact level, not just full/empty?

The Plus Uni has an analog input: with a suitable level probe it can read the fill percentage, not just two states. That path uses a small script.

Summary

• Yes, the Plus Uni works: the clean-contact float goes to a digital input and it alerts your phone.
• It needs low-voltage power (9-28 V DC), not 230 V.
• One float = one alert; for empty and full, two floats on its 2 inputs.
• Alternative: the Plus i4 DC if you want up to 4 inputs.

Tell us about your tank (which float you have, whether you want one or two alerts, whether there's a pump) and we'll confirm the setup and which power supply fits so it arrives ready. Technical support and shipping available for your market.