Two back-to-back mass shootings have left America on high alert. 

The FBI is warning of the possibility of copycat shooters, saying to be especially aware at movie theaters, shopping malls and other public places. 

It seems like nowhere is safe. 

There was panic in Springfield, Missouri, where a 20-year-old man, identified by police as Dmitriy Andreychenko, was arrested after he walked into a Walmart wearing body armor and carrying a loaded rifle. He claims he had no intention of shooting up the store, but charges are pending against him.

In Tampa, Florida, a man drove a golf cart into a Walmart, hitting patrons as he went. Others were forced to jump out of the way to not get hit. Michael Hudson, 56, was hospitalized after crashing the cart. He will be booked into jail after he's released from the hospital, authorities said.

And in Orange County, California, a man went on a stabbing spree, killing four. Suspect Zachary Castaneda, 33, has not given a motive for the rampage. He is expected to face multiple charges when he is arraigned. 

So what's being done to make sure people stay safe? Saks Fifth Avenue has installed gunshot sensors that trigger alarms if a weapon is fired.

"Within about a second, a second and a half, everyone in the building knows where the shooter is," Christian Connors, CEO of Shooter Detection Systems, told Inside Edition. 

The Wall Street Journal also reports that employers are stepping up security and active shooter trainings so that staffers know what to do in the event of an emergency. 

Security expert and former FBI agent Bob Strang, of Investigative Management Group, said everyone needs to be prepared.

"It's important to have a plan no matter where you are — at work, at home, Times Square, church," Strang told Inside Edition. "You need to know where your exits are, you need to know what to do if something were to happen."

He added: "If something does happen, you have to run. If you can't run, you have to hide. If you can't hide, you have to fight."

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