well without knowing what your lock on your door looks like we're not going to know if it's a mortice or not, so have a look at this and see if your lock matches any of these.
I can't post a direct link but if you go to thelocksmith.ie and the mortice deadlock page you'll see what i mean.
If you have a look on Google you will find this for mortice deadlocks and note the keys are quite distinctive and would definitely be my preference from a security point of view: