arduno power off

hey,guys i was wondering that is there a command to switch off arduino after a particular condition is met :o 8)

No, unless you use a relay or a circuit to interrupt the power supply.

In case you don’t mean what you seem to can you please explain why you want to turn the Arduino off.

You can use a self latching relay circuit and let the arduino switch it off. Using sleep mode might be an alternative

No need to turn the Arduino off, just stop it sending the message.
Set a global variable such as messageSent to false then

  if(SEN_input == HIGH && messageSent == false)
    messageSent = true;
    rest of your code here

Call the exit() function?