This article is about emergency alerts for the general public. (Mercer ARES has an alert system for its members and is part of its own emergency communications plan for Mercer ARES.)
Everyone should have a battery powered radio and batteries that work so you can receive information in an emergency.
Government agencies have always wanted a method to warn citizens about emergency situations. This became more important during the Cold War between the United States and the Soviet Union. The US government had a plan to sound air raid sirens when they detected incoming nuclear missiles. The plan was to "Duck and Cover" http://en.wikipedia.org/wiki/Duck_and_cover when you saw the flash.
The most common alerts are for severe weather. Alerts could also be issued for toxic gas or other dangerous substances released in an accident. Acts of terrorism are another possibility. I have received alerts for rabid wildlife in my area as well as malfunctions at the water treatment plant. You could be sleeping when a tornado rolls through.
Television and radio stations are part of the Emergency Alert System http://www.nws.noaa.gov/om/NWS_EAS.shtml previously known as the Emergency Broadcast System. Cable television systems also transmit these messages. The system is tested periodically. You have probably seen or heard the tests. They consist of annoying sounds followed by a message or text crawl on the television screen.
I know people who don't own a television. In general, people don't always have the television or radio on. This is a known limitation and government agencies have been working on other ways to alert citizens.
NOAA (National Oceanic and Atmospheric Administration) operates the National Weather Service. For many years now people have been able to purchase Weather Radios to receive reports of impending severe weather, like tornadoes. The radios can be set to activate based on SAME (Specific Area Message Encoding) codes. You can program some of these radios to activate just for the areas and types of alerts you choose to receive. The National Weather Service has expanded their system to be an All Hazards alerting system for more than just weather. http://www.nws.noaa.gov/nwr/
Municipal, county and state governments may have systems too. These are usually some kind of Reverse 911® system. If you have an emergency you dial 911 on your telephone to get help. The Reverse 911® system goes in the other direction.
The Reverse 911® system calls your telephone in an emergency with a recorded message. Usually this system will try to call all the land-line telephones in the affected area. They get this information from the telephone company so there is no need to register. This only applies to land-lines with listed numbers. If you have an unlisted number or use a cell phone you should register with your Reverse 911® system.
It gets a little complicated with Reverse 911® . Mercer County maintains a Reverse 911® system for people whose municipality does not provide one. Currently the municipalities that have their own system are: Trenton, Hamilton, Lawrence and Princeton Township.
What if you don't have a land-line telephone and you use a cell phone? You will have to register your cell phone number in that case. Usually you can also register to receive email or text messages. Sometimes this is done directly by the government and sometimes it is done through a third party.
Colleges and Universities may also have a system in place to alert faculty and students. Businesses may also have a system to alert their employees. I am focusing on the general public but you may have additional options too.
Other ways to receive information can be through Internet services like Twitter and Facebook. You will have to check to see if your government agency is on one of those services.
There are many ways to be alerted and I can't know all the different ways that may be used in your particular area so I encourage you to research them on your own. You may want to register for alerts where you live and where you work.
Will these systems guarantee that you are notified? No. There are many ways these systems could fail or be overloaded. Many people will be notified and you will very probably be notified one way or another, sooner or later. Some people will be notified before others. They can't call everyone at the same time and your phone may be be busy but they will make several attempts.
I have researched some of the ways to be alerted for residents of New Jersey, Mercer County and some of the municipalities in Mercer County. Some of the municipalities allow you to register your email address for newsletters. I don't know if they would use that for emergencies too. Some of them allow you to register for telephone messages, SMS text messages and email specifically for emergency messages.
Some of the links below go to the main web page and you will have to find the link for emergency alerts or whatever it may be called. In other cases I have linked to the page with the emergency alert information. Pages may move so be prepared to do a little digging. If you find a broken link please let me know.
State of New Jersey
Municipalities in Mercer County
NOAA All Hazards / Weather Radio
Emergency Alert Radio Stations (EAS)
Reverse 911® is a public safety communications system developed by Cassidian Communications, formerly PlantCML, a unit of EADS North America. It is used by public safety organizations in Canada and the United States to communicate with groups of people in a defined geographic area. The term is a registered trademark in the United States.