I am an engineer at a machine shop. When a machine stops running, I want to be notified via a vibrating pager (like at restaurants). My plan is to attach the arduino board in the machine and when the machine stops (quits vibrating) I want it to trigger the vibrating pager that I have in my pocket. By what means can the arduino communicate with the vibrating pager to cause it to go off? SMS? Wifi? Bluetooth would likely be out of range. Other options?
To do SMS through a GSM shield like https://www.arduino.cc/en/Main/ArduinoGSMShield with a dataplan, and the device should be accessible anywhere you can get reception. With a wifi shield like https://www.arduino.cc/en/Main/ArduinoWiFiShield101 you could make it work within your wifi network.
Sparkfun's sales guide at https://www.sparkfun.com/pages/wireless_guide indicates there are a few bluetooth modules that reach 100m, so if your range is less than 100m, bluetooth is a possibility.