My battery keeps draining

My car will start and run fine until the next morning I go to start it it's drained flat and it makes this beep noise every 10 minutes. I shut off everything and all doors are closed and it makes a noise all night long and battery drained and needs jump next morning. What could it be? I'm a single mother and can't afford to just bring it in and get charged for them to tell me what the noise is. All car place say they need to do a diagnosis test and that cost money, so any information would be greatly appreciated. Thanks