Alright! So the idea struck out of blue one day when I was shocked to see someone sitting outside my office enjoying reading a newspaper!
I had no idea who this person was, when did he come and since how long was he enjoying his unsolicited stay just outside my cabin? You must be thinking what a fool I am but you gotta trust me on this, my office is one of the creepiest that one can get anywhere. Seriously! (I hope my boss never reads this;-))
Anyhow, I decided to do something without spending anything north of INR 500/- (Approx $6-7). I had an Arduino Uno clone ready at my disposal. So, all that I needed was an ultrasound sensor, and a Buzzer. Rest of the steps, circuit assemblies, software code are ensued in this tutorial. I hope this would excite few electronics newbies out there.