I hate idiot lights and have no use for alarms, etc. There I said it! What I do like is GAUGES! Luckily my boat came with gauges for water temp, oil pressure, etc. Not that gauges are absolutes, they can be miss-calibrated as my most recent tach experience has shown. What gauges offer is the ability to establish a "norm", as in, the needle "usually" shows x, y, or z. When it does not, that is the time to start paying attention. Since most marine diesels are industrial based I've always been skeptical of worries about oil pumps breaking, etc. These engines are very robust and last for 1000's of hours. If they are running they tend to keep doing so. A pressure gauge would go a long way in diagnosing your problem. That said, I'm guessing the engine was hot, the oil is halfway used or due for a change, and the pressure dropped low enough to trigger the alarm. The alarm may not do this again until the engine good and hot and the oil broken down from use. Was the oil level in the normal range on the stick or a bit low but still okay? Sometimes just a 1/2qt can make a difference. If the engine has some hours on it, this could simply be a case of clearances being a bit worn. Not a big deal at all if the engine runs well, but below the alarm threshold sometimes. I'm guessing you are running a 15w-40 HD diesel rated oil? You probably should be. If you are you could also switch to a straight 40wt HD diesel oil if you are in a temperate to warm climate. The straight 40wt will be more stable at running temp. RT