Is there a ready-made door sensor?

What I'm looking for is specifically the type of sensor where somebody passing through an open door will cut a light beam (or Infra-Red) and cause something to happen.

In my case, a motion sensor will not do what I want - it could detect somebody near the door, but not going through it. It could also detect a pet moving.

I need to situate the sensor high enough that a person would trigger it, but a cat would not (unless it is riding a unicycle or walking on stilts). The door is normally open, so magnetic switches are not an option.

To make it simple to install, it should have a light source and sensor in the same unit, with a reflector at the other side of the door. Making one is, of course, an option - but buying one would be a lot easier.

I have seen commercial units online, but for the price, I believe they must be diamond encrusted platinum.

Reflect sensor.

https://www.google.ca/search?q=reflect+sensor&rlz=1C9BKJA_enCA739CA739&hl=en-US&prmd=isvn&tbm=isch&tbo=u&source=univ&fir=bnTsQSG9NRWXnM%3A%2Cm-rw8sfRI76OdM%2C_%3Bxol9-NYhFNR4hM%3A%2CU9PLE0KxB9rcqM%2C_%3B9HQ7SrKnqTLVqM%3A%2Cy-iL8h5Wpt75kM%2C_%3BtMRFbRBS-QMZ-M%3A%2CDNhvbbYLeFis5M%2C_%3BlNzjS2G_PGIrSM%3A%2CIxxR4BJMA5piKM%2C_%3BVKDE8PRruyTeHM%3A%2Cy-iL8h5Wpt75kM%2C_%3BKFW2IG_8s59DFM%3A%2CqTdbRNccnJK4_M%2C_%3B1Ghf9QfMOUC0EM%3A%2CHlHwd-y7dWN2_M%2C_%3BV5Ss9XHFE4SYIM%3A%2CTMdXnN9C9ysyMM%2C_%3BUMHuBJtv66_PBM%3A%2ClYw8DdBjG6RjRM%2C_&usg=__Qm0tN76nR0Fn9vn2kEaj7OAxD18%3D&sa=X&ved=0ahUKEwj2lYjf5JPVAhVFxWMKHWerDXsQsAQIPg&biw=1024&bih=748

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Do you just need it to chime or do you want to do something with the data?

Motion sensors are perfectly usable if you just limit the cone of detection. You're ruling out a whole area of technology because putting a piece of tape on the sensor isn't something you considered.

(Modulated) IR LED & detector on one side of the door, small reflector on the other side. Or, like Adafruit seems to prefer, sensor and detector on opposite sides. Very simple and cheap.