At Google, I worked on Nexus Imprint, Android’s first fingerprint sensor system debuted with Android 6.0 Marshmallow. Fingerprint detection may be used to unlock a device, sign in to apps, and authenticate in-app purchases.
I was the design lead within a trifecta core team comprised of a product manager and an engineering lead.
I designed the entire UX flow, provided creative inputs to other designers, collaborated with internal teams (e.g., Google Wallet) and consulted with external partners (e.g., LastPass).
As the OS, it is Android’s responsibility to keep user data secure. Existing screen lock options were overly complicated or not secure enough. Only 45% of Android users protect their data with a screen lock. Common reasons cited were the inconvenience of using a screen lock or don't care enough. We saw an opportunity to improve security and I was tasked to design the fingerprint experience on Android.
Sensor Placement UX Implications
There were 4 different sensor location proposals and I evaluated the UX implications –
Front of the device
Too many buttons in proximity to each other (Android already has permanent buttons at the front for Back, Home, and Recent).
Combined with the PWR button on the side
This implementation can lead to the most undesirable UX. People tap on the Power button to turn off the screen when they want to dismiss a phone call or is done with a task (e.g., after checking notifications). If this is also the fingerprint sensor, people will be asked to tap on that same button to make an authorization (e.g., authenticate a purchase). However, people might tap on the button to dismiss the screen similar to dismissing a phone call. In that case, they would have inadvertently authorized an unwanted purchase.
A separate button on the side
The main disadvantage of a side sensor is the hardware's limitation imposed on the sensor size. The thinness of mobile devices is a competitive advantage and the sensor will need to be very small. When the sensor is small, it takes more steps to register a finger. For instance, the one I tried took 20 taps to fully register a finger.
Back of the device
This is what we shipped. It's the most ergonomic choice. This is the only button in the back so it's very easy for the finger to identify without looking.
People might be setting up fingerprint after unboxing their brand new device. Make a good first impression by providing a speedy setup process.
Help people find and adjust to the sensor location. They should be able to find and tap on the sensor without turning their device around to look for it every time.
Provide UI and tactile feedback when interacting with the sensor.
Material Design Guidelines
I published the Material Design Guidelines for internal teams and external companies as a reference as they integrate Nexus Imprint into their products.