My Honda was like this. You can lock it if you hold the drivers side door handle up from the outside and then hit the automatic lock, but it takes effort and would still keep you form lockign the keys in your car.
At least my Honda was that way, not sure if yours will work that way.
Anyway, point is, I was always worried about losing that key, and they told me when I bought the car that if I dropped it repeatedly or knocked it around a lot, that could mess it up to make it not work too.
Another thing that I found out later, was that when my battery started going bad in the car, my key would not always work to start it. We figured this one out on our own. We kept getting that little key light in the dash and the car wouldn't start, but if you took it out and tried again it would work.
We finally replaced the battery just because it was getting sluggish about starting and that fixed all problems with the key.