Lame, this works only for a minute. The traditional methods work for hours
Clean the keypad. Wait for next person to enter the pin. Whip out your Sherlock Holmes equipment consisting of fingerprint powder and fingerprint brush. You are not only going to learn which keys were pressed, you can retrieve his fingerprints too. Additionally you can also retrieve his DNA.
Endless hours of fun follow. Create a fingerprint replica to lock/unlock your own iPhone. Have the DNA analysed for medical conditions etc.