寝るときは必ず鍵をかけてください。

to lie down; to go to bed; to lie in bed; to sleep (lying down); to sleep (with someone, i.e. have intercourse); to lie idle

regular (stops at every station) Jouetsu-line Shinkansen

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

always; without exception; necessarily; certainly; without fail; positively; invariably

key; lock

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to hang (e.g. picture); to hoist (e.g. sail); to raise (e.g. flag); to sit; to take (time, money); to expend (money, time, etc.); to make (a call); to multiply; to secure (e.g. lock); to put on (glasses, etc.); to cover; to burden someone; to apply (insurance); to turn on (an engine, etc.); to set (a dial, an alarm clock, etc.); to put an effect (spell, anaesthetic, etc.) on; to hold an emotion for (pity, hope, etc.); to bind; to pour (or sprinkle, spray, etc.) onto; to argue (in court); to deliberate (in a meeting); to present (e.g. idea to a conference, etc.); to increase further; to catch (in a trap, etc.); to set atop; to erect (a makeshift building); to hold (a play, festival, etc.); to wager; to bet; to risk; to stake; to gamble; to be partway doing ...; to begin (but not complete) ...; to be about to ...; indicates (verb) is being directed to (someone)

to give; to confer; to bestow; to kindly do for one; to oblige; to favour; to favor