ORLANDO, Fla. - In a sign of how jittery the nation has become about terrorism and gun violence, major theme parks on Thursday installed metal detectors at the front of their attractions.

In Orlando, Walt Disney World would not say how long its metal detectors would be in place. SeaWorld said it had installed the devices as part of enhanced security for the holidays. Universal Orlando said it was testing using them as guests approach the theme parks.

The changes extend outside Orlando. Disneyland and Universal Studios in Hollywood are also installing the detectors.

Security in general has been a big concern after recent attacks in Paris and San Bernardino, Calif. On Wednesday, the Department of Homeland Security issued a bulletin saying it was "especially concerned that terrorist-inspired individuals and homegrown violent extremists may be encouraged or inspired to target public events or places." It said the public should expect to see more police and more stringent security at public places and events.

Disney World - where a man was arrested last weekend after trying to enter the Magic Kingdom with a gun - is now discontinuing the sale of toy guns. It is also banning people 14 and older from wearing costumes, even at Halloween parties.

Universal spokesman Tom Schroder said the decision to test metal detectors was not driven by a specific threat. "We want our guests to feel safe when they come here," he said in an email.

SeaWorld said in an email that it would be "enhancing security measures for the busy holiday season.