Between 2011 and 2014, emergency calls to San Francisco’s 911 call center rose by 28%.

This surge pushed San Francisco’s 911 center past its normal bounds, BBC reports. Hiring remained flat, and so during busy periods operators were forced to work overtime.

This extra strain on the system didn’t come from any rise in crime, or in the occurrence of natural disasters, but rather from a much more mundane source: butt dials.

In a report by Google, first covered by the BBC, researchers found that 30% of all 911 calls coming from cellphones in San Francisco were butt dials. This builds on previous research by the FCC that estimated that 50% of the emergency calls in New York City from mobile phones were pocket dials.

While this might at first seem amusing, when you dig into 911 protocol, it becomes clear how much a burden this is on operators. Operators can’t easily tell the difference between a butt dial and a situation where someone has gotten the phone knocked out of their hand by an attacker, or are somehow incapacitated.

This means that 911 workers have to follow up with every single butt dial they get. In the study, it took operators an average of one minute and 14 seconds to determine whether or not the call was a butt dial or a true emergency.

And you need to multiply that number by a lot to find the stress on the system. "If my anecdotal experiences are remotely accurate," FCC Commissioner Michael O'Reilly wrote, "it would mean that approximately 84 million 911 calls a year are pocket-dials.’

Part of the issue is that all cellphones are required to have allow 911 calls without unlocking the phone. While this measure makes it easier for people to make emergency calls, it also greatly increases the possibility of a butt dial.

But the ease of butt dialing has saved at least one life. An 18-year-old man in Mufreesboro, Tennessee was recently able to make a 911 call while trapped under a truck — all because of an accidental Siri activation.