Many many photos.....few results

I'm curious about something. Perhaps a better informed viewer out there can enlighten me. On the old spy camera I had over 900 shots that showed nothing but the interior of the house, however, the camera was only activated by movement, supposedly. Now with the new spy camera, I'm over 100 shots. Once again just showing either my wife or I walking through or just the interior of the house. What is activating the camera? Our walking through the room certainly; but what about the rest of the time? Any sleuths out there have a good answer?