What is the problem?
Is there any way to stop a print straight away?
What did you already try to solve it?
Turned power off or waiting for the the web to stop the print.
Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, octoprint.log, serial.log or output on terminal tab, ...)
It would be nice to have a input either a physical button or a button on the web gui to stop the print straight away.
How quickly your printer responds to an emergency stop M112 code is up to its firmware. A lot of printers will simply ignore it during nozzle / bed heating if using the "heat and wait" command. For this reason, an emergency power shut off button you physically press will be the most effective and possibly the most reliable solution.
Never rely on any piece of software during an actual emergency such as a fire, get something that physically cuts power to the entire system.
For me, hitting that cancel button is usually enough these days. When I first started out though, I had a big red button on the front of the printer that cut power to the printer for those nice head crash emergencies. It definitely is the better way to stop the printer.
Agreed with @PythonAteMyPerl and @WarHawk - killing the power is the best option for an emergency stop. If you're remote and need to kill the power, you could set up a relay board to control the power to the printer and use that to kill the power to the printer immediately. There's loads of folks who have done this and documented how online, and I believe there are Octoprint plugins which help ease integrating a relay board with the Raspberry Pi.
In terms of a big red button, something like this looks like it could be good.