Developer Francesco Pavanetto, who shared the app on Reddit, says he tuned the vibration to the actual measured pitch of a real cat purr and built it so the pattern never repeats exactly. If you’re worried about downloading an app outside the App Store, Pavanetto says PurrPad is signed and notarized, so you shouldn’t encounter Gatekeeper warnings. I wouldn’t keep it running all day, but for cat lovers who enjoy that soft, subtle vibration when their cat purrs, PurrPad is a surprisingly convincing stand-in.