Apple was awarded a new patent on Thursday for a system that can check a user’s identity by measuring their heart beat and comparing it to on-device records. A future Apple Watch could use the technology to authenticate the wearer and enable security features like Apple Pay.

The catchily-titled “User Identification System Based on Plethysmography” would save users having to tap in a four-digit code. Right now, the code is requested every time a new wearer puts on the watch, but this patent could automatically start measuring the user’s heart beat by checking the gyroscope and accelerometer. When the wrist is raised, the watch could start the process without needing to touch the screen. Presumably, you’d be able to use the technology to unlock your iPhone, too.

The system uses a pulse oximeter to shine two lights through the skin. The amount of light reflected tells the watch how much blood is present at each point, which can then be used to determine the heart rate. This data can be used to identify defining characteristics about a wearer’s blood movements.

The recently-released Apple Watch 2 can measure heart rates under water.
The recently-released Apple Watch 2 can measure heart rates under water.

AppleInsider notes that the current watch uses a similar pulse oximeter to the one described, so in theory a software update could bring the system to older hardware. That may not be possible, though, if Apple does not have a way to securely store the health data. Unlike current readings, this data could be used to grant access to the device, requiring the utmost levels of protection to avoid it falling into the wrong hands.

The process falls under the category of biometric authentication, measuring a user’s body to check their identity. Other examples include fingerprint and iris scanners like in the Samsung Galaxy Note 7. Many of these systems suffer from the same benefits and pitfalls. For example, there’s no password to remember, but unlike a password, you can’t change the data associated with your body.

Photos via Apple, Getty Images / Chris McGrath, Giphy