At the moment, the best way to log in to macOS without having to type out a password is to buy a MacBook Air or a MacBook Pro with a Touch ID sensor above the keyboard. It’s present on all Apple laptops now, though it’s not yet an option on desktop Macs, and it’s not possible to add it on the desktop by buying an accessory.
If you do have a MacBook laptop with Touch ID available, you can open up the Apple menu, choose System Preferences, and then select Touch ID and Add Fingerprint. Up to three fingerprints can be added per user, and you can also use the biometric security method to make Apple Pay purchases on your Mac besides using it to log in.
When you next get to the login screen, all you need to do is place your finger on the sensor and you should be granted access (if there are several user accounts registered on macOS, you may have to select yours first). Fingerprint data can be removed or replaced by going back to the Touch ID screen.
The other password-free option is to use an Apple Watch—this works on both desktop and laptop Macs, and with all recent versions of the Apple Watch (check the supported models here). Open the Apple menu, then choose System Preferences and Security & Privacy, and tick the box marked Allow your Apple Watch to unlock your Mac.
As long as both Mac and Apple Watch are signed in to the same iCloud account, Wi-Fi and Bluetooth are both turned on in macOS, and the Apple Watch has been configured with a passcode, you’ll be signed straight into your account when your Apple Watch is brought close to your computer.
Android lets you log in to your phone using your face or your fingerprint, though Android being Android these technologies are implemented in slightly different ways depending on the make and model of your phone. Your handset might have both of these options, but at least one of them should be available.
In the case of the Google Pixel phones, if you open up the main Android Settings app and then choose Security, you can see the options available on your device—tap on one of them, such as Face unlock, to get it configured.