Car spontaneously locks it self while parking

Something is wrong with my prius...

While the car is off in parking it is randomly and spontaneously locks itself like someone is pressing the lock on the remote key. It can happen few times a minute.
The auxiliary battery is OK, I even connect it to battery charger just in case and it is still happening (while charger is connected).

How can I debug it? where should I start from?

Thank you !

 

BTW, I put the remote key far away from the car just to be sure it is not "crazy" remote.

 

Update...
The spare remote key is the source for the problem. I thought it is far away but apparently it is not enough.
This spare remote key battery drained a month ago and I replaced its battery. After that it didn’t work, I.e when pressing the lock /unlock it was not doing nothing. I didn’t had the chance m to check it and put the key in a drawer inside the house. Today, when looking at it I see that it is the problem and locks the car in randomly manner.
I remove its battery and apparently the problem solved.

Did someone had such thing were the remote controller gone crazy ? It started first as not functional after battery replacement and then this phenomena.

Thank you