Wireless driveway alert system

The way my house was designed it is a split level. In the cold New York weather it keeps out all that winter wind that can hit it. With the smaller windows though I can't see whose pulling in the driveway until they're knocking on the door. So last week I stopped at Harbor Freight and picked up a wireless driveway sensor. If anybody pulls in it sets off a tone to make me aware of the people first.