Dic: listen for

• We listen for footsteps approaching. 
• They're both asleep upstairs, but you don't mind listening just in case of trouble, do you?
• I didn't really listen out for the lyrics.
• I will have to let you in the front door if you come home late. I will listen for you.

1. VERB | If you listen for a sound, you keep alert and are ready to hear it if it occurs. 
2. to try to hear someone or something. 

Cf.
VERB | If you listen to someone who is talking or to a sound, you give your attention to them or it: He spent his time listening to the radio.
VERB | If you listen to someone, you do what they advise you to do, or you believe them:
Anne, you need to listen to me this time. When I asked him to stop, he would not listen.

.... Cobuild, http://idioms.thefreedictionary.com/listen