A simple rule to check whether a verb is transitive or intransitive (requires a direct object or not): Ask the question What or whom for example I opened ... (what did I open?) I opened the window. Window is the direct object. "I opened" is not a complete sentence, the object is missing! Therefore to open is transitive verb which requires an object I called (whom?) I called him to call is transitive verb to rain, to snow: it rained, it is snowing : These are complete sentences and the verb does not require an object (intransitive verbs). likewise to sleep, to wake up etc. are intransitive verbs.

Follow the link, the explanation is very clear here. http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv244.shtml

Well, there are two ways... 1) Look at the full sentence and see if an object immediately follows the verb. If a preposition follows instead, then you can be sure the verb is intransitive. (Minor exception: following verbs in the infinitive form. The full sentence structure will clarify the meaning.) 2) Check a dictionary - decent dictionaries will tell you whether a verb is transitive or intransitive (or, in some cases, both).

Use a dictionary? http://www.macmillandictionary.com/