battery window/door sensor

[Akatar]

i own 14 door/window sensors.
two of them i bought a half year ago, secondhand
these two drain batterys
about 1 ever 2 months, the other door/window sensors a working for more then a year now.
what can be the reason that these 2 sensors using so much power?

both windows opened once a week or so

[b_weijenberg]

Is the auxiliary contact enabled and open?

[Akatar]

nope, not in use
switch 2 and 4 off are off