When Marnie goes into the basement, her ankle bracelet starts chirping that she is more than 100 feet from the transmitter, when in actuality it is only about 20 to 30 feet above her head.
The director makes a point of showing that the steps up to Marnie's front door are covered in fallen leaves, implying that no one has lived there for a long time, but earlier in the scene the street's trees still have their leaves.
The whole ideal of the "100 feet" is wrong. One-hundred feet is a length equal to the height of a 10-story building, so from the transmitter to the front door or the basement is well under the "100 feet" she is allowed to go.
Shanks wouldn't have (or at least shouldn't have) been assigned to the case. Since his deceased partner was the victim, there would have been a conflict of interest.