Every summer I worry about the water temperature in my aquarium. A hot room can affect the tank as well. I installed a cooler above it, but having to turn the cooler on and off by hand was inconvenient.
Initially I thought about buying a separate aquarium temperature sensor. Then I realized I already had something that measured temperature in the same room: the air conditioner. SmartThings could read that value, so before buying another device, I wanted to reuse information already available from a sensor I owned.
Does a sensor need to be used only for its original purpose?
During summer, our air conditioner has power and can provide an indoor-temperature reading through SmartThings. Some smart buttons also have temperature sensors, but I chose to try the AC data first.
My reasoning was simple. If the AC had already cooled the room sufficiently, the aquarium cooler might not need to run as often. I treated the room's air temperature as one supplementary input.
I did not add another display or device beside the tank. The AC supplied the measurement, while a smart plug controlled the cooler's power.
Adding a Zigbee plug made the action straightforward
I connected the cooler to a Zigbee smart plug that I could control through SmartThings Station. The core automation was to switch on the plug when the room temperature exceeded a chosen threshold.
The particular threshold is not the point of this story. Homes differ in indoor conditions, tank size, animal species, and cooler performance. Giving a single temperature here as though it were correct for everyone would be misleading.
I hoped that when the room cooled down, or the AC sufficiently cooled the space, the cooler would need to operate less often.
Air temperature and water temperature are not the same
This approach has an important limitation. The AC displays the temperature of the surrounding air, not the water inside the tank. Water temperature can change differently because of tank size and placement, lighting, flow, and the cooling method.
The automation must not be understood as a safety system that guarantees correct aquarium water temperature. When keeping living animals, independent water-temperature checks and suitable emergency safeguards take priority. Consider what happens to their safety if the smart plug or internet connection stops working.
Also verify whether the fan or cooler automatically restarts when power returns, and whether the plug's rated load and operating conditions are suitable. Electricity near water requires particular attention to moisture and leakage risks.
My setup was strictly an example of supplementary control using existing sensor information. Understanding that limit actually makes the idea more useful rather than less.
Sometimes automation means running something less often
We often imagine a smart home as something that starts more actions and operates devices more frequently. But reducing unnecessary operation can also be worthwhile.
If the AC is already cooling the room, the cooler might have less reason to keep running continuously. If that decision can use an existing measurement, adding more sensors may not be necessary.
I did not measure and record how much operation time this saved, so I cannot quantify any savings. The useful insight was not a proven percentage of reduced runtime, but that a status value from one device can become an input for a different device.
I did not connect everything with Zigbee
I preferred Zigbee when choosing switches, buttons, and plugs, but I replaced the boiler controller with a Wi-Fi-based unit. There was a specific reason: the manufacturer's cloud service supported account linking with Samsung SmartThings.
The controller connects through Wi-Fi to its manufacturer service. After linking that account to SmartThings, I could also operate the boiler from the SmartThings app. I liked not having to constantly switch between different apps just to control the home.
My real goal was never to make every device use Zigbee. It was to bring devices with different communication methods into one practical control environment. Compatible switches and plugs paired directly with the hub through Zigbee; the boiler depended on a cloud-to-cloud account integration.
That cloud connection does leave a dependency on the manufacturer's service. After my earlier experience with a discontinued Wi-Fi plug service, I cannot ignore that risk. Even so, at the time, the ability to control the boiler within SmartThings was the decisive factor.
The AC supplied temperature data for the aquarium cooler; a Zigbee plug switched the cooler on; the boiler used a different route but appeared in the same common interface. Not everything had to share a protocol to provide a useful, unified routine.
Before buying another sensor, check what you already have
Now, when thinking about an automation, I first look for information the devices I already own can provide.
Temperature, door state, light state, and motion are all possible conditions. But just because a value exists does not mean it should control something automatically. I need to ask what it actually measures, how reliable it is, and what happens if it is wrong.
That matters especially when the outcome involves animals or electrical safety.
A smart home is not only about adding devices. It can also be about finding new uses for information already available.
In the final article, I will describe a different input: a CCTV person-detection event that switched on floor lighting in a particularly dark living space.