The id100-20 and id100-50 ultralow-noise single-photon-counting modules for the visible spectral range have been released by id Quantique SA. They offer a dark count rate of less than 1 Hz and of 20 Hz for devices with 20- and 50-μm diameters, respectively, and provide a fiftyfold improvement in signal-to-noise ratio, according to the company. As with other versions in the series, the modules feature timing resolution of 40 ps, dead time of 50 ns, timing stability up to count rates of 20 MHz and compatibility with many acquisition instruments. Their response function is free of artifacts or satellite pulses, making them suitable for time-correlated applications. Both free-space and a fiber-coupled version are available.