Some changes have been made in Danbury schools to keep a closer eye on student whereabouts after an elementary student left school on his bicycle at dismissal time instead of waiting to be picked up.  According to a newsletter sent to district residents, staff and safety advisers will be stationed at the correct places with ample time for arrival and dismissal.  Students are assigned to various rooms for dismissal if they are walkers or get picked up and district officials say there will be closer supervision when they are moved.  A new security system, called Raptor, was implemented Monday where all visitors must present proper identification to a security guard at the front desk.  A visitor badge is printed, and guests must check out before leaving the building.