The original sound was written in 1983 using C, and consisted of around 20,000 lines of code. Fortunately now that we have the Web Audio API and this excellent post on how to recreate Deep Note using SuperCollider, things are a bit easier.
I wanted the sound to be similar enough without being exact. Much like those adverts on TV that use music that sounds roughly like a popular song that they haven’t paid for the rights for. Here’s what I ended up with. (Chrome/Opera/Safari/Firefox only)