Police scanners are cool idea to have so you can monitor troubles at their start.
Also lot of big troubles started with small and later escalated into chaos, so it make sense to watch it.
Some of the big happenings here started with small fights at the sport events. Even some of the last rioting that lasted for days here started with peaceful protesting of 200 workers, but then someone call people over the Facebook to give support and then someone throw the stone and that s it.
You never know.