Yaris 2007 remote entry doesn't open (it only closes)

[nicorac]

I've made a little step forward.

I measured the cell battery: 2.9v (ok, with no charge attached, anyway...)
I tried cleaning the button with contact cleaner: no way.

Then a lucky break: pressing the Unlock button twice really quick it worked, all of the times.
When I say really quick I mean really quick, say 2 presses in less than 0.3 seconds.

It seems some kind of security feature