When the party line was already in use, if any of the other subscribers to that line picked up the phone, they could hear and participate in the conversation. Eavesdropping opportunities abounded. If one of the parties used the phone heavily, then the inconvenience for the others was more than occasional, as depicted in the 1959 comedy film "Pillow Talk". Dialing one's own number and hanging up would make all phones on the network ring, resulting in the residents on the system (sometimes a half a dozen or more) all answering the phone at the same time; this was sometimes used as a form of prank call, but could also be employed as a form of early warning system for the immediate area, a user could alert all local residents at once. Party lines were typically operated using mechanical switching systems which recognized certain codes for revertive calls; these no longer work on modern electronic or digital switchgear.