Every holiday season, several of YouTube’s most prominent makers get together for a Secret Santa gift exchange. It is always fun to see what kind of tailored gifts they create and this year is no different. Sam Battle of the LOOK MUM NO COMPUTER YouTube channel drew Ali Spagnola in the most recent exchange. Ali likes both music and exercise, so Battle built her this quirky drum machine controlled by the user’s heartbeat.

At first glance, this looks like a fairly conventional drum sequencer. It cycles through eight beats and can play from five different samples. Each beat has a set of five switches to select the sample to play on that beat. But the twist is that the machine only moves to the next beat when the user’s heartbeats, as opposed to moving through the sequence at a consistent rate.

That sounds a little bit jarring, because hearts are not metronomes. But the benefit is that the tempo increases with the user’s heart rate, so the pace matches their activity level.

An Arduino Nano board detects the user’s pulse through a Pimoroni Pulse Sensor. It plays drum samples (or any audio clips) loaded onto a SparkFun WAV Trigger module. Battle wired the sequencer switches in a keyboard-style matrix, which reduces the number of IO pins required to just the number of rows plus columns instead of one pin for every switch. On each beat, the Arduino checks the switches and then plays the corresponding drum samples. Finally, Battle crammed all of that hardware into an enclosure with 3D-printed decoration that makes the device look like an oversized heart.

This isn’t something you’d ever see on a store shelf, which is what makes it the perfect gift for one maker to send another.