Personally answering the door for your parent:
Rebbe Avahu stated: One should honor his parent as did my son Avimi. My son Avimi had five sons in the lifetime of his father, and nonetheless when his father Rebbe Avahu would come knocking on the door, he would personally run up the door to open it up for him even though he could’ve had one of the sons do so. He would also acknowledge his father’s presence right away and as he was running to open the door, he would tell him that he was coming to open it.
 Kiddushin 32a