This paper presents a new technique for detecting chip alterations using intrinsic light emission in combination with electrical test. The key idea of this method is based on the fact that any active device emits infrared light emission when it is powered on. High sensitivity photon detectors can be employed to capture the weak emission while the chip under test is powered on and electric stimuli are applied to it. In particular, two main families of electrical test modes, static and dynamic, can be applied. Positive results of the application of this methodology as well as key challenges will be discussed in the paper, including spatial resolution, imaging processing, data interpretation, etc. © 2011 IEEE.