What is the part marked with a 205?

[fixit7]

What is the yellow part with the 205 on it?

The whole circuit is the detector part of a laser alarm.

The alarm goes off if the laser beam is interrupted.

https://www.dropbox.com/s/esho9ia2oj3mbnz/Laser_Detector_Circuit.png?dl=0

https://www.dropbox.com/s/i5g3qrd5s09mfqa/Laser_Detector_Circuit2.png?dl=0

The photo detector is an awful small surface to have to aim the laser at.

If possible, I would like a photo detector with a larger area.

It works inside, but I have not tested it yet on my patio where the ambient light is much brighter.

Thanks.

[Nerull]

A 2 meg trimpot.

[james_s]

If you need a larger area for the detector, use a lens, if you can find a small Fresnel magnifier that should work well. Keep in mind the larger your detection area, the more sensitive it will be to ambient light too.