it took a little while for them to get used to the idea that the were not
allowed down this hallway.  Both front door  has a long hallway to them.
at first they would venture to a point the screech is chirped once than if
they don't go back across the line it does it again  than stays on constant
till the area is clear.  I just have to remember to shut it off when I take
one to the vet so they don't freak out when I cross the line.
when it goes off they take off away from the line doesn't hurt them.  the
only thing  I worry about is if something scares one of them and they make a
beeline for the door than it chirps it will scare them out the door.  But it
has not happened and luckily there is a screen enclosure at the front door.
the cats happy stay on the Florida room in the back and leave the front door
alone.

cost varies anywhere from $100 to $5000 depending on what you have  can be
it is mainly for outside designed to keep varmints out of gardens areas the
projector sits next to the door has a range up to 30 feet  wireless sensor
eye just like a photo light    plugs into the wall  you come with in the
range sensor goes off once for 2 seconds  with in 5 seconds if the sensor is
still on it remains on till the field is clear.  the reaction is the same as
a dog repeller