Steady beep coming from under the hood

I have a 2008 nissan altima coupe. It hasnt been started or driven in probably over a week we came outside today and a steady loud beep is coming out from under the hood. It can be heard from at least 50 feet away. It sounds like it is coming from the driver side up against the fire wall its been going for hours we finally just pulled the battery terminal to shut it up. Started the car with no issues and the sound continues. Any ideas