My 2009 Mazda 6 GH alarm goes off only in the spring summer is on the car, why?

No answer for you, but I would love to know myself as mine has started doing this too!

Heat/hot air triggering the ultrasound sensors? I have the same problem on a 2010 GH Mazda 6 EU model. Alarm going off randomly, especially at night. Suspected weak car battery and replaced it. This worked for a while and the problem came back. (I put the old battery in my old 205 where it has been working perfectly.) The car is drawing a small current when the car is switched off. This drains the battery and triggers the alarm. I suspect this may be related to the Bluetooth module as the alarm issue occurred around the same time that the Bluetooth stopped working. Something is drawing enough current to slowly empty the battery. SOLUTIONS: 1. Overnight: lock the car with the key instead of the key fob. This appears to not set the alarm but the battery still drains slowly... 2. For longer periods I disconnect the battery. Anyone had the same issue? Has anyone found the solution for the battery drain?

Take out the fuse for the horn. There is a youtube video on disconnecting some wires on the left side of the trunk but I haven't tried it yet.