On iOS, 5 quick presses doesn’t call emergency services, it reverts your phone to a pre-login state and gives you emergency options.

This is super helpful to know if you have biometrics enabled. And cops can’t hold your phone in front of your face to unlock it if you do this.

Try it if you have iOS. 5 presses quick, you’ll feel a vibration to let you know it worked so you can do it from your pocket.