A.T. Robertson Commentary Acts 12:14

"And when she knew Peter`s voice, she opened not the gate for joy, but ran in, and told that Peter stood before the gate." — Acts 12:14 (ASV)

When she knew (επιγνουσα). Second aorist (ingressive) active participle of επιγινωσκω, to know fully or in addition (επ), to recognize. She knew Peter and his voice from his frequent visits there.

For joy (απο της χαρας). From her joy (ablative case), life-like picture of the maid who left Peter standing outside with the door to the passageway unopened. Note the aorist tenses for quick action (ουκ ηνοιξεν), εισδραμουσα (from ειστρεχω, defective verb, only here in the N.T.), απηγγειλεν.

Stood (εστανα). Second perfect active infinitive of ιστημ, intransitive, in indirect assertion with τον Πετρον (Peter) accusative of general reference. The slave girl acted as if she were a member of the family (Furneaux), but she left Peter in peril.