Techniques for fast and accurate measuring test strip intensities are disclosed herein. A cassette attachment device for detecting intensity of a test strip cassette includes a strip chamber configured to accommodate at least a portion of a test strip, a light source configured to provide illumination to the test strip cassette via indirect lighting, an attaching mechanism configured to attach the device to a mobile device, and a camera window configured to transmit light signal reflected from the test strip cassette such that the mobile device can capture an image of the test strip cassette illuminated by the light source.