How to get rid of annoying ding/beep noise in Mazda Tribute- 2001 model?

Does anyone know how to get rid of the ding/beep noise you get when the keys are left in the ignition? It doesn't just beep when the drivers door is open, it's any of the passenger doors & boot also. We recently went to the drive-in & wanted to open the boot & sit in the back, but to do this we had to sit with the beep noise through the whole movie, because you listen to the sound through the radio, it is highly annoying!! If you know how to cut it off it would be greatly appreciated! Thanks :)