CONCORD -- A Concord neighborhood, including an elementary school, was placed on lockdown Monday morning after residents discovered suspicious hand grenades that were later determined to be replicas, police said.

The owners of a home on the 2300 block of Ranchito Drive were cleaning out their garage about 10:45 a.m. when they found what appeared to be grenades in the depths of their storage, Lt. Darrell Graham said. The homeowners moved the grenades into their house before calling police, who arrived and confirmed that they could possibly be dangerous devices.

Police evacuated the home and asked the two adjacent homes to shelter in place, Graham said. Preschool-age students at nearby Sun Terrace Elementary School were held in lockdown from 10:52 a.m. until they were allowed to board early buses home at 11:55 a.m.

The bomb squad from Travis Air Force Base arrived to take possession of the grenades and found they were replica devices, Graham said. The all-clear was given at 1:48 p.m.

Police advise residents to immediately leave the area any time they encounter a suspicious device, whether or not they think it is a real threat.

"If you locate a suspicious device, immediately evacuate the house and call from somewhere else," Graham said. "Do not handle the device, whatever it is -- a grenade, a device with wires. They should be left in place to let us do what we need to do."

Contact Erin Ivie at eivie@bayareanewsgroup.com. Follow her at Twitter.com/erin_ivie.