鍵(かぎ)が掛(か)かるto become locked (e.g. of automatic locking)

泥棒(どろぼう)：「くそっ、鍵(かぎ)が掛(か)かっている！」

Thief: "Damn, it's locked!" {to become locked (e.g. of automatic locking)}

鍵(かぎ)が掛(か)かっているのでこの部屋(へや)には入(はい)れません。

Since the key is locked, you cannot enter this room. {to become locked (e.g. of automatic locking)}

強盗(ごうとう)は鍵(かぎ)が掛(か)かっている店(みせ)の扉(とびら)をぶっ壊(こわ)したそうだ。

It seems that the robber destroyed the door of the store that had become automatically locked. {to become locked (e.g. of automatic locking)}

自動的(じどうてき)に鍵(かぎ)が掛(か)かるそのシステムは安全(あんぜん)を保(たも)つのに効果(こうか)的(てき)だ。

That system, which automatically locks, is effective in maintaining safety. {to become locked (e.g. of automatic locking)}

オートロックのドアは勝手(かって)に鍵(かぎ)が掛(か)かってしまうので、注意(ちゅうい)が必要(ひつよう)です。

Because the auto-lock door becomes locked on its own, caution is necessary. {to become locked (e.g. of automatic locking)}