With smart thermostats like Nest and Tado, it’s easy to set a temperature for your home and let the technology take care of it. We’re also starting to see the introduction of individual smart thermostats for each room – at a price, of course.

But if you just want a low-cost way to monitor the temperature of a particular room, getting iPhone alerts if it falls outside your chosen range, the $30 Sense ThermoPeanut may be for you …

As gadgets go, it couldn’t be much simpler: pull out the plastic tab to activate the battery and it automatically starts the pairing process via Bluetooth. Open the free iPhone app, hit the ‘Add’ button and wait for it to connect.

Once connected, it will display the temperature in the iPhone app, and allow you to set an acceptable temperature range. If the temperature goes higher or lower, it sends an alert to your phone anywhere within Bluetooth range. You also get graphs to track the temperature over time.

Right now, that’s all it does, but the company is promising Nest and IFTTT integrations next month.

The device comes with sticky pads that allow you to stick them up almost anywhere. They are also very light, at 7.5g, so any double-sided tape would easily do the job if you want something more permanent. It’s also very small at 1.7 inches high by an inch wide and 0.19 inches thick.

You can connect multiple ThermoPeanuts to the same iPhone, and the company reckons the replaceable CR2032 watch battery lasts around six months.

The range is listed as up to 200 feet, which is the standard theoretical range for Bluetooth. In use, I found I could get readings from my office anywhere in the house.

I do have a couple of complaints about it. First, while it’s available in a range of colors, you can’t choose what you get – the company sends you a random color. That seems a shame, when people may want to match their decor.

Second, based on comparing with another thermometer I’ve found to be reliable, the ThermoPeanut over-read the temperature by between 1.5 and 2 degrees. That’s obviously not ideal, but so long as it does so consistently – which it seems to – you can at least factor that into your settings.

For most people, I suspect a tolerance of 1.5-2C isn’t going to be critical, and there’s probably a limit to the accuracy you can expect in a $30 wireless device. As someone whose home has a 2C temperature gradient between the downstairs living room where the thermostat lives and my upstairs office, it’s handy to be able to check the office temperature from anywhere in the house, so it’s still on my wall.

The Sense ThermoPeanut Smart Wireless Bluetooth Thermometer is available from Amazon for $29.99.