Smart WiFi Pool Thermometer Options

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For swimming pool owners monitoring the water temperature of the pool coming into, and during, the swimming season is not only useful, but can be important for maintaining the appropriate chemical balance. This is commonly done with a conventional pool thermometer, often one that floats in the pool itself.

When we installed a swimming pool, it was a smart home no-brainer to be able to ask the house what the pool temperature was so I embarked on finding a connected pool sensor that could be queried by a voice assistant or smart home platform. This would most likely require a WiFi pool thermometer of some kind in order to connect and check temperature readings.

Temperature sensors are undeniably a basic staple of the smart home and there are many to choose from. Indeed, these sensors are so cheap that they are often just thrown into other unrelated devices like light switches or motion sensors. As such, it was surprising to find nothing for swimming pool owners.

Yes, there are many floating wireless pool thermometers that signal back to a remote LCD display or even a smartphone app, but these are completely standalone devices that don’t use standard WiFi. These digital thermometers are usually pretty cheap and won’t last. Things are starting to change though, and there are some options to get some smarts into your pool maintenance.

Smart Swimming Pool Sensors

Looking at off-the-shelf devices that have some level of smart home integration there is a lot more going on in the European market. For some reason there is a greater presence of smart pool devices there than presently in the US, although some new US startups are looking to change that such as Sutro but they still don’t support integration at this point. One option that is readily available, though, is the Sonoff TH16 smart switch.

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Sonoff TH16 Smart Switch

✔ Supports Alexa, Google Home, IFTTT
✔ Water Temp
✔ WiFi, no hub required
✔ Lowest Cost
✔ 100-240V input

✘ Needs hard wiring for power
✘ Needs weather protection

The Sonoff TH16 paired with the DS18B20 water proof temperature probe can get the job done with minimal upfront cost. While it is primarily a smart switch rated up to 15 Amps it includes the temperature probe to allow for automated control of whatever it’s connected to. It’s easy to install using the terminals on one end, but you can skip the output if you just want to use it as a WiFi pool thermometer. You could, of course, use this as a temperature triggered switch to control something like a pool heater or even a pool cover motor.

I like the idea of using a water temperature probe like this as you can immerse it deeper into the pool water instead of just getting the surface temperature. Floating pool thermometer devices can suffer from this, shall we say optimistic measurement, especially when you’ve had a pool cover on for a while.

The main catch is that the device itself is not water proof, and it requires hard wiring for power. This means you’ll likely need to install it into a waterproof enclosure. That’s not a huge problem as these are commonly available and inexpensive, like this one. Be sure to get one that is IP68 waterproof rated. Going with this kind of DIY solution will still be the cheapest option available, and covers the most common automation platforms.


Ondilo Ico

✔ Supports Home Assistant
✔ Water Temp, ORP, pH, Conductivity
✔ WiFi and Bluetooth, no hub required
✔ Rechargeable long life battery
✔ Trend alerts to prevent problems
✔ Pool and Spa / Hot tub versions

✘ Expensive

The Ondico Ico floating pool sensor is an example of one of those European devices, and includes some very nice design innovations such as individually replaceable sensors and a low profile that works under an outdoor pool cover or in the skimmer if you want it out of sight. There are also separate versions for pool and hot tub installations.

This one isn’t just a floating WiFi pool thermometer, but a chemical sensor that also monitors pH, chlorine (via ORP measurement) and salt level. On board smarts enable it to not just report problems, but also to alert you to trends that will lead to imbalances so you can address them beforehand.

The Ico is powered by an internal rechargeable battery which is charged via a USB port under the UV resistant top cover. Ondico says a single charge will last you the whole season.

Ondico only lists European resellers on their web site, but they ship internationally and have a US support number available. While they don’t state official smart home support, Home Assistant has device support available in their plugin library.


WaterGuru Sense

✔ WiFi, no hub
✔ App based graphs and alerts
✔ Water temp, pH, chlorine, flow rate
✔ Skimmer adapters available

✘ No smart home support
✘ US only

The WaterGuru Sense is an automated swimming pool monitoring system that replaces the cover of your skimmer and monitors pH, chlorine levels, water temperature, and pump flow rate. This data is transmitted back to your smart phone on request and presented in some very nice graphs and offers free cloud storage so you can check on your pool anytime.

The sensor hangs from the lid into the returning water flow and uses replaceable cartridges that last about 3 months, suitable for chlorine or salt water pools but not hot tubs. This approach ensures you’re getting the water temperature flowing through the system and not just the surface temperature. The electronics are all up top, powered by standard C cell batteries which should give you about 6 months before replacement is needed. By default the lid fits 8” skimmers, but they offer an adapter for other sizes, and a square option is also available.

While there is no smart home integration on offer here, if you want to be able to monitor and check on your pool status at any time this could still be the easiest option for you. A caution for swimming pool owners outside the US though; it’s not supported internationally, and the app is only available in US app stores.


Blue Connect Plus

✔ Supports Alexa, Google Assistant, IFTTT
✔ Temp, pH, ORP, and Conductivity
✔ Floating or Integrated pipeline install

✘ WiFi needs optional Extender
✘ Most expensive option

The Blue Connect offers a comprehensive floating pool sensor package as an alternative to the Ondilo Ico, but with more common smart home integration options, including Amazon Alexa, Google Assistant, and IFTTT support. It also sports some cool options, such as including a pipe fitting to allow it to be installed inline with your filtration system. It does have a higher profile, however, which makes it unsuitable for skimmer placement or use under a pool cover.

There are cheaper models available, but this Plus Gold package covers all the bases by including lifetime access to their software platform (normally a subscription), and supporting conductivity for salt water pools. If you don’t need that you can drop down a tier. The Blue Connect normally utilizes Bluetooth. If your pool is too far from the house for Bluetooth, the Blue Extender provides a more typical WiFi gateway option that is also required for the supported smart home connectivity.

US buyers may find it difficult to get hold of right now. While the blueriiot site has a US page, it doesn’t offer any buy options. You’ll need to go through the European or Australian pages to get an option, or you might need to look for a retailer that carries it.

What About HomeKit?

None of these commercial offerings support HomeKit, so what if you’re after something that talks to Siri? There are a couple of options here, but they are less conventional. The first is the nearest I could find to an off-the-shelf product, the second is to go DIY.

Netatmo Conversion

✔ Supports Alexa, Google Assistant, HomeKit, IFTTT
✔ WiFi via parent weather station
✔ Water Temperature
✔ Drop in probe for skimmer

✘ Needs Netatmo Weather Station
✘ Subject to availability


The guys over at the Pool Thermometer site have been doing interesting things with smart home weather stations to address the lack of WiFi pool thermometers in the market. They’ve done a few different mods over the years, but this one is their current all rounder.

It’s basically a Netatmo Weather Station outdoor module that has been stripped down and encased in a water proof sheath so that what normally monitors air temperature can be immersed in the water. Custom wiring has been added to run back to a weather proof box to hold the battery pack for easy access, and an antenna to get the signal out of the water.

This option supports all the major smart home platforms via the main weather station unit, but you need to buy that separately as this is just the outdoor module. Of course it can only make use of the water temperature sensor as the other data (humidity and air pressure) from the unit are meaningless from under water.

A DIY Homekit Pool TheRmometer

DIY sensor box

DIY sensor box

When I was looking at solving this problem, the pool thermometer mods available at the time didn’t support HomeKit so I had to come up with another way. The key hurdle to over come was needing a temperature sensor that could last a long time on battery power inside a water proof enclosure.

That necessitated finding a device that used something other than Bluetooth as the range from the pool to the nearest Home Hub would be likely too far. WiFi devices would also be out of the question as the power requirement would be too high for such an installation.

There were some options using Fibaro Z-Wave door sensors, but that would necessitate integrating a Z-Wave hub with HomeKit. That’s do-able, but an expensive option just for this project. Having a Philips Hue bridge provided an alternative option.

The Hue Motion Sensor includes an air temperature sensor that appears automatically in HomeKit and is a relatively inexpensive ZigBee device. That protocol would allow it to relay data using the mesh network of my smart lights, and would run on batteries for 2+ years.

Keep in mind that you need to have other Hue lights to bridge the gap between your Hue bridge and the pool skimmer box. These could be Hue Calla outdoor lights, some of Hue’s outdoor fixtures, or even just a basic Hue PAR38 bulb if you have a socket close enough.

I have Hue Calla path lights around the pool area, so they take care of this in my case. All I needed to do was find a suitable enclosure that was large enough for the sensor, but small enough to fit in the skimmer box. After much hunting I found one with the necessary IP67 rating.

After setting the sensor up in the Hue app, I half filled the box with crushed stone as ballast and nestled the sensor in the middle. This step is necessary to weight the box down so it sits low in the pool water. You want it as low as possible to get the most accurate reading without being submerged as the water would block the ZigBee signal. Keeping the seal above the water line also helps ensure longevity.

Parts Required:

I’ve found this solution to be reliable, as it’s survived two full swimming seasons so far. The only issue is that the temperature sensor doesn’t get a good read from inside the box, but it has been a consistent under read of about 4 degrees. That makes it easy to correct with a Siri Shortcut. Note that Water Temperature is what I named the motion sensor in the box, you can call it whatever you want.

 
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This shortcut simply gets the current reading and corrects the 4 degree error before reporting the result. Now I can just ask Siri to “Check the pool temperature” and get the answer I was looking for.

If you don’t have a Hue system, you’ll need a Hue Bridge and at least one light to configure the system, so it bumps the cost up. If you do have a Bridge set up already, however, this is probably the cheapest way of getting your water temperature via Siri.

As an aside, I have also had limited success doing the same kind of DIY setup using an Eve Weather device. You’ll likely need an Eve Extend to get the Bluetooth signal to go far enough, but even then the pool needs to be close to the house for it to reach. Using an Eve device has the nice bonus of logging the pool water temperature readings in the Eve app in a nice graph. It works, but has been significantly slower to respond than the Hue Motion sensor approach. You’re experience will very much depend on placement and distance to the Eve Extend or Home Hub.

Frequently Asked Questions

Is there a pool thermometer that connects to Alexa?

Yes, there are a few smart pool thermometers that connect to Alexa. These need to be some kind of WiFi pool thermometer in order to communicate with Amazon’s servers, your Alexa device, or the Alexa app. In this article we cover which models are currently available and their pros and cons, as well as some DIY approaches that can get the temperate reading to Alexa.

Are pool thermometers accurate?

The temperature sensors in wireless pool thermometers are generally accurate, and some models may offer a degree of calibration. Placement is particularly important in these cases, where a floating pool thermometer may give readings that are warmer than the actual bulk of the pool water due to solar heating on the surface, pool covers, or direct sunlight on the thermometer itself.

Where possible it’s best to place the pool thermometer in the skimmer to keep it both shaded, and to get it measuring the water flowing through the system for better accuracy.

How long do you keep a thermometer in the pool?

Wireless pool thermometers are designed to be left in the pool throughout the swimming season, as are most basic floating models. If you only want to temporarily test the water temperature with a thermometer you’ll need to leave it for at least 10 minutes to ensure time for the temperature reading to stabilize.