Purchased after having a cable cut and two bikes stolen at a campground. Instructions are clear although at first glance there appears to be allot of buttons and stuff to remember, it really was quite simple. You can pick your own code and set sensitivity (2). There are 4 small batteries which are nearly impossible to stack up and get in there small housing one at a time. I found it easier to simply scotch tape them together and then install like one battery. There is nothing to tell you battery life depending upon how it's set up (motion sensor on or off) I guess time will tell. Alarm is loud enough to send a bike thief running. I see no way to defeat this unit other than cutting cable (will sound alarm) or I suppose one could just simply smash it with a hammer so don't leave it close to ground, of course this would make some noise. Cable is short only 24" so locking several bikes together might be difficult but it's the motion your hoping for. All-in-all Looks like a good deal. In fact I am buying another for my friend. 4 stars because I do not know and they wont tell how long the expected battery life is.