Laser Point Receiver

this circuit called as laser point receiver, this circuit can in applying at system keaman of house in the place of from resistor photo. if it is compared to resistor photo, hence nicer phototransistor. principal from this circuit much the same to with principle from resistor photo, that is if there are incident light into phototransistor hence resistance of the phototansistor low, so that can overcome current , otherwise there are light entering hence high phototransistor resistance. So current will be overcome U1 and strengthened again at U2 causing can animate speaker.