Using time-resolved emission to measure electrical signals inside very-large-scale integration complementary metal-oxide-semiconductor circuits in a non-invasive fashion is a very powerful technique. However, node scaling and the related supply voltage reduction have created significant challenges. In this paper, we investigate the limits of established and prototype single photon detectors for future low voltage applications. In particular the performance of a state of the art InGaAs single photon avalanche photodiode and a superconducting single photon detector are reported and compared for low voltage applications using test vehicles fabricated in IBM 65 nm silicon on insulator technologies. © 2011 IEEE.