Have you ever had a child who got sick in your classroom and you couldn't take care of him by yourself? Has a child ever needed to be restrained and you needed an extra pair of hands, but no one was near? Have you ever thought "I need to call for help, but I can't think of the phone number to dial?" If you see this as a need then let me give you the system that works for our school.
Each staff member has one of these cards taped to the wall in their room near their door. When they need extra help (Not the kind of help that would be needed if you called 911), they send a responsible student to the office with this card. This alerts the office staff that they need to send someone to your room immediately (sometimes it is the secretary if no one else can be found).
Please remember to leave a constructive comment so I know if I'm fitting your needs.