How your phone knows it's your finger

1. 0:00 The question
2. 0:04 Electricity, light, sound
3. 0:15 This phone uses sound
4. 0:21 Ridges and air
5. 0:26 The echo
6. 0:39 A map of ridges
7. 0:44 One map, then recognition
8. 0:55 Template, match, limit
9. 1:10 Three readers, one answer