2006 mazda 6 doors automatically lock sitting still with no buttons pushed
 

so I just got this car replaced fob batteries and noticed after I parked it in garage shut it off and set key on work bench a min or so later the doors locked all on there own. Why and how do I stop this? I rolled window down made sure car was unlocked set key in seat and the doors locked once again so if I leave key inside walk away somewhere ill be locked out. Any ideas?