How to prevent alarm from going off??

Hi so I recently bought a used car.  I have no
problem with it but every single time I use the key
to unlock the door.  The notification panel starts
telling me to start the car so the alarm will not go
off.  It drives me crasy I have people waiting for me
to unlock the door for them but first I have to start
the car before I do that.  If not the alarm will set off
just the emergency lights go off but no noise.  Can
someone tell me what I can do to fix that..