Biff(2015) pays for his taxi ride to the McFly household with his thumbprint. When the ride ends, a synthesized voice gives the price one-seven-four-point-five-zero. The taxi driver presents him with a book-sized device with the price at the top on a red 7-segment LED display. Biff presses his thumb on a reader at the bottom that glows white as it scans. When the payment is verified, the thumbprint reader and the price go dark as a sound plays like a register.
For due diligence, let me restate: multimodal biometric or multifactor authentication is more secure.