While 1999’s Blair Witch Project was the movie that kickstarted the found footage horror craze of the 2000s, it’s Paranormal Activity, released a decade later, that has proved to be the subgenre’s biggest longterm success. While Blair Witch remains a horror classic, it proved to be a one-off in terms of popularity, and the initial sequel and the more recent reboot were both commercial disappointments. Paranormal Activity, however, spawned an extremely successful franchise, with six movies so far and a seventh due next year.

So why did Paranormal Activity have such an impact when so many post-Blair Witch found footage horrors were quickly forgotten? Much of it is down to its pure, brilliant simplicity. Director Oren Peli was not some cynical producer looking to cash in on a popular craze. He was a software developer with no prior filmmaking experience, who simply had a great idea that was relatively easy to execute. A couple experience strange, scary noises in their house, so set up video cameras to record overnight to find out what is causing them. The tension that builds as we watch this nighttime footage, waiting for something sudden to happen, is masterfully done. It’s so simple and effective that it makes you wonder why it hadn’t been done dozens of times before.

Inevitably, the Paranormal Activity sequels have varied in quality, and while they all have effective moments, none of them quite capture the scares of the first movie. They are all part of the Hollywood horror machine, something the original film absolutely wasn’t (initially at least). And the story behind its journey to the screen is a fascinating one, with festival rejection, different endings, a delayed release, and ultimately, a huge commercial victory for the filmmakers. Paranormal Activity can be streamed right now on Netflix, and here’s our guide to this terrifying modern classic.