@JeffyPoooh
Leave the house, close the door - oops, I just left my password on the door handle. Get on the bus, pay the fair - oops, I just wrote my password on a coin that I gave to the driver. Go shopping, touch the 'I brought my own bags' icon - oops...
Now that I have left my password everywhere, I had better change it. There is only one place biometrics should be used: people should only be allowed into the house of commons if they have the hand or eye of an MP.