Usually yelling, "Hey!..........Folks!" works for me.
There's another teacher in our building who uses a different "F" word, surrounded by "Shut," "the," and "up." I wouldn't have believed it, if I hadn't seen if for myself, but he gets away with it. I guess because he's been around so long, handles graduation practice each June with over 200 kids and yells that into a bullhorn to get them started, they're used to it.
I read one technique that works if your adminstration lets you is threaten to keep the class for a minute or more after the bell rings if you have to count to 10, three times in a row.
You stand up in front of the class and say "when I hold up my finger i want everyone quiet and looking at me. If I have to raise three fingers then the class will stay after the bell rings to give me the lost instructional time that I had to wait for you to be quiet."
it doesn't work will all classes because some of my students would rather stay in my class than leave, but we have strict tardy policies so it normally is effective.
The students who are paying attention will get their peers to be quiet because they don't want to be kept after the bell rings.
I normally only have to keep them once for them to quiet down when I raise my hand.
I use PAT (in other words known as earned free time). They earn 4 minutes / day, I have 4 lines on the board symbolizing the minutes. When things don't go well, I start erasing half a line or a line (30 seconds or 1 minutes). It's surprising how much they care and they tell each other to shut up. The worst thing I end up doing is actually erasing a minute. No yelling, no threatening.
I notice a lot of people say they wait and won't talk until the kids are quiet but I feel like this only works if the kids are relatively respectful of the teacher. Some teachers might be waiting until it's time to retire.
I watch a teacher do this everyday when he is teaching in my room during my plan. He says "I'll wait until everyone is quiet." But, many of the kids just keep on talking because when he's quiet they feel that's the best time to talk since they aren't talking over him. I watch them argue with him that they aren't being disrespectful if they are talking while he's quiet because he's not teaching.