Has anybody tried tiny commercial space stations as sensor pickets?
Thinking about the problem of how to provide long-term sensor presence with low ongoing costs. Obviously these stations would have very limited capabilities since they are limited to commercial sensors, but they also should be very cheap and small, and you could probably carry them in a hangar to drop at points of interest.
Yes, many have done that.
Another option is to make bouys. A bouy is a missile with sensors, no warhead, no engine, and no fuel. The reactor will keep the sensors going forever and missiles have no upkeep, so bouys are a cheap way to monitor small locations. Ships can drop the bouy out of a missile launcher, or you can put the bouy on top of a transfer stage. The former requires the ship to travel to the destination to be monitored, which is fine for jump points but can be contraindicated for planets. A bouy on a missile can travel to a planet on its own, and no real harm is done if something shoots it down.
When I use bouys I design my survey ships to carry a few on missiles and few to be dropped off at jump points.
Unless you're going for deep space locations DST installations are probably the regular way of handling this problem. However, a tiny picket station could be easier to transport.
Deep Space Tracking systems can have a lot of range, but they are quite a lot heavier than a bouy or a civilian station. You also have to place them on a body, which means it will orbit and get out of position. That makes them more situational. Not necessarily useless, however.