Peugeot 206 lx 1.4 (2003) - Peugeot 206 - Double warning beep - dan.hall

You'll have to bear with me on this one. This is my first car, and I haven't had chance to pick up the owners manual yet (literally been driving it for 5 days). Its a 2003 Peugeot 206 1.4 lx, had a lot of work done to it over the last year or so by a mechanic who sold me the car himself such as new clutch, tyres etc. Car runs fine, so far as I can tell from my experience in a car this far. Only issue is the double warning beep which happen every 15/20 minutes or so, and I have really no idea what I should be looking for. A bit worrying when I don't know what it is, if it's potentially reporting a fault. There seems to be a red light on the dash, above the oil temperature gauge. I'm not sure if that's normal either? Basically, how do I go about diagnosing this one? A good place to start even? Browsing around forums, warning beeps seem to be a particularly irritating issue with the 206, especially since the beep sometimes occurs when there is no fault. I'm sure i'll be a bit more confident with issues like this once I've got some real driving time in, but right now I'd rather not take the chance and just ignore it. Any ideas? Thanks!

Peugeot 206 lx 1.4 (2003) - Peugeot 206 - Double warning beep - dan.hall
Ok, the red light above the engine temperature gauge is the handbrake indicator, I am an idiot. But I can confirm the warning beep is actually 3 beeps long (unless I'm actually hearing different warnings) and when it sounds theres no message from the dash computer and no warning light on the dash. At a loss, but suspecting its a dodgy door sensor...maybe.
Any ideas? Still looking for help!