In all the places we have lived in Mumbai, the door is designed in such a way that it does not need a key to lock it(it locks automatially on shutting) but needs a key to unlock it from outside. Such a mechanism is doomed to lead to the circumstance of key being left inside the house and I and saurabh have experienced this on numerous occasions.
And I have always wondered, why is a lock with in built key not a popular thing in the human civilisation.
Infact, why we still use the same lock and key that probably Tipu Sultan used? I know that the technology has really evolved to swipe cards, to fingerprint scanners to retina scanner, password based locks but common man still believes in good old lock and key. Though these days the lock is in built to the door - the traditional model still stays. And even though it is cumbersome to carry key everywhere, I wonder why is the dependence on an external key still popular.
And well the first advantage of a simple method of having a lock and key is that, the key is not a function of the owner of the house. Unlike in fingerprint and retina scan, where the previously authenticated person has to himself be present, in this method, they need not be present everytime to open it. Passing on the key to someone else is a situation we encounter a lot in our day to day life hence I think this is where most of the time simplicity works.
So one design guideline must follow while designing a new lock and key device is that: Key should be transferrable.
Now then we can use a password alright. But what if we have to give a key only once. I mean, I can give the password to my friend (who is medium trust worthy) but now the danger will lurk that he might get in anytime as he has the key. So if we use password, we give away the password permanently (unless we change it and that is a tedious mental process). So a key should not just be transferrable, but transferrable temporarily which means, that there has to be expiry on it.
Apart from that a simple thing with lock and key is that if we lose the key, we can create another key. We need not break the lock. Example if I had a fingerprint scanner and I lose all my fingers to a traditional indian bandit called angulimal, then will i have to break the lock to get it reset? And the lock is expensive right?
Which brings us to two points: The lock and key should be cheap and the loss of key should minimize lock destruction.
Any more reasons?