In very low light conditions Sentinel-A’s dot will become very difficult or impossible to see. This was an intentional decision made during development. Sentinel is designed for every day carry and maximum battery life. Although it never fully shuts down, Sentinel-A is designed to get very dim while being carried concealed, underneath covering outer garments like shirts. Carried on the right side of the body, either appendix or hip, or carried cross-draw on the left side of the body, the light sensor will face towards the body, creating a dark environment where the dot gets very dim and draws very little battery power. As soon as you draw your pistol, the brightness adjusts to ambient lighting conditions almost instantly—even the quickest draw in the west wouldn’t be able to outrun the brightness adjustment time. This strategy allows us to get two years of real world battery life from a CR2032.
But what about those super low light situations? Our opinion is, if it is too dark to pick up the dot, it is also likely too dark to take a legally justified self defense shot. You need to be able to tell a judge and jury that you knew your target, what was behind it, what was in front of it, and clearly saw an imminent threat to your life. Blazing away in the dark is not advisable. If dot brightness in very low light concerns you, we recommend attaching a weapon light to your pistol or training with a hand-held light. The sensor picks up reflected spill from the light and dot brightness will increase. To really cheat it, you can use a hand held light with a neck index, and some of the light from the flashlight will hit the sensor directly. This gives you a very bright dot just as soon as you hit your flashlight, and a legally defensible view of what exactly you are aiming your pistol at.