Question On Electronic Locking Systems

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I have a networking room which I want to lock using an electronic lock although I am not sure which one I should get. The door of my server room is currently equipped with a not electronic keyed entry door knob. I do not want to drill any additional holes into my door for the new lock which I get and want to be able to have access to the door using a number combination or a physical key. Are the types of locks which disconnect the outside knob part in order to lock better (if you try to turn it when locked it will turn but have no effect on the latch) or the type which does not allow for the knob to turn better? I am thinking to install the MiLocks Satin Nickel Electronic Entry Door Knob (Model # TKK-02SN) although suggestions for different models are accepted in this thread. My networking room is one of the rooms which need to be protected more although being able to be accessed easily, therefore I want to purchase a new lock which would have a keypad option.