Battery shouldn't run flat in that short period of time, I have left my Fatboy Lo for about 3 weeks without riding it and its starts straight away.

Security system shouldn't drain the battery in that short time.

Possible crook battery, also you may need to have the charing system checked to make sure the system is charging at the correct output

This may not be a fix for your current problem, have you condisered using a battery tender to trickle charge your battery when your not riding for long periods, use this device on my bike also my partners bike as well my bike is 2yrs old at the end of this year and her bike is over 2yrs old with the original battery.

battery on mine is 5 years old and mine still starts even if its been parked in the shed 2 to 3 weeks 

g'day,  it does sound like your battery is on the way out.  just remember that if you keep trying to start the bike on anything lower than the 11 volt you are going to F*** your starter really quick.  the starter will burn the contacts and plunger out at best.

Mate, do you use a piece of plywood under your stand? If not do it. Battery will leak to the concrete.

Hi I had this happen to my 08 superglide.. Took it back to the dealer they found the battery to be stuffed and replaced it under the warranty.. They told me because they are
a sealed unit harley cover them under the warranty.. So take it back to the dealer.. To get them to check the battery might get it replace.. Never had the problem after that..

 Maybe the volts are less likely to fall out if the bike isn't leaning so far over...