The remote starter and security system from Subaru has multiple sensors. One is somewhere on the transmission to ensure that it is in neutral before you start the arming sequence. If you leave the shifter in first gear when you park it won't allow you to start the engine remotely.
If you accidentally set it off by having the remote in your pocket or in a handbag, there's no way to know from the remote itself that your engine is running. However the engine will shut off after a default ( but configurable) time span of 15 minutes.