Service workers
Thieves posing as service professionals may obtain access to a residence. They'll tell you that they need to look at your gas or electric meter, that your internet service needs to be adjusted, or that they need to take a reading inside your house.
If a service person shows up unexpectedly, be polite, ask for their information, and explain that you need to reschedule because the company hasn't alerted you of their coming. You can then contact the company they claim to represent. Of course, if you phone your provider and they don't have any information about the visitor, there's a good possibility the caller was a thief trying to break into your home.
Even real workers can be questionable in some instances. They casing residences throughout their labor and return for your valuables later. Alternatively, they could tell a buddy which residences are the best and whether or not they have security systems. The worker can leave an unlocked window or unusual symbols to indicate which house to target for their accomplices.