How to start an Activity from a Service?

Even if the framework allows you to start an Activity from a Service, it's probably not a proper solution. The reason is that the Service task may or may not be the focus of the user at the time the Service wishes to interact with the user. Interrupting what the user is currently doing is considered bad design form, especially from something that is supposed to be operating in the background.

Therefore, you should consider using a Notification with Notification Service, which carries a PendingIntent to launch the desired Activity when the user decides it is time to investigate. Think of it as delayed gratification.

I had a problem starting an activity from a service, it was due to the missing FLAG_ACTIVITY_NEW_TASK intent flag.