In an emergency, call 911 or your local emergency number immediately from any wired or wireless phone.
An emergency is any situation that requires immediate assistance from the police, fire department or ambulance. Examples include:
Important: If you’re not sure whether the situation is a true emergency, officials recommend calling 911 and letting the call-taker determine whether you need emergency help.
When you call 911, be prepared to answer the call-taker’s questions, which may include:
Remember, the call-taker’s questions are important to get the right kind of help to you quickly.
Be prepared to follow any instructions the call-taker gives you. Many 911 centers can tell you exactly what to do to help in an emergency until help arrives, such as providing step-by-step instructions to aid someone who is choking or needs first aid or CPR.
Finally, do not hang up until the call-taker instructs you to.
If you dial 911 by mistake, or if a child in your home dials 911 when no emergency exists, do not hang up—that could make 911 officials think that an emergency exists, and possibly send responders to your location. Instead, simply explain to the call-taker what happened.
More Information:
http://www.911.gov/whencall.html