What causes PP3 battery energy depleation ?

I have a Schlage PP3 battery powered number coded lock for my garage. When the battery is depleated I have a key to open it from the outside. If I use an alkeline PP3 battery it will need to be replaced after one month. A friend of mine has the same lock and he tells me that his PP3 alkeline battery lasts for at least three years. Is there any way for me to decect if the lock unit is drawing excessive energy from the battery because of some short circuit in the internal componants of the lock.
Any help will be appreciated
Regards
Tom T