We are in the thick of a brutal heatwave, which means I am currently playing my favorite seasonal sport: the Window Game.

The rules are simple but high-stakes: you trap the cool air inside all day, and then you wait for the exact moment the outdoor temperature drops below the indoor temperature to fling the windows open.

The trouble is timing.

Up until now, I’ve been relying on the hourly forecasts from the national weather service. But generic city forecasts aren't exactly tailored to my street. My backyard can easily bake a few degrees warmer than the official report, and when you’re desperate to cool down a house, every single degree counts.

Time for a quick weekend project.

The Hardware Setup

A few years ago, I built papercal, a little application that displays our family calendar on a paperd.ink e-ink device. As luck would have it, I had a second one of these devices just lying around in my parts bin.

Since the heavy lifting of the codebase was already done, swapping out the calendar UI for a temperature display was a breeze. My goal was simple: show the forecasted temperature on one side and the actual, real-time temperature on the other. Paired with our indoor thermostat, I’d finally have the perfect data dashboard to win the Window Game.

Finding a Hyper-Local Data Source

There was just one catch: I don’t actually own an outdoor thermometer. To get true backyard accuracy, I needed a hyper-local data source. I started digging through online weather maps with crowdsourced weather stations. I found a public Netatmo weather station practically sitting on my doorstep. It almost certainly belongs to one of my neighbors. (If you’re reading this, neighbor, thanks for the free data!)

Enter papertemp

And so, papertemp was born, a quickly hacked-together weekend project that puts the current forecasted and live-measured temperatures side by side.

Now, with just a quick glance at the screen, I know exactly when it’s safe to crack the windows and let that sweet, cool breeze roll in.