My friend just moved into an apartment which was previously occupied by an older man in a wheelchair. He had some changes made to the apt, one of which was an automatic motion sensor faucet in the bathroom. She says it worked every other time she was there, but now that she's moved in it doesn't work.

There's a red light that blinks intermittently on the faucet, regardless of any motion. There's a gray Moen branded control box (about 6x3x3 inches) under the sink with funny hex screws on it. There are bathtub-style hot and cold control knobs also under the sink, as well as the traditional smaller on/off controls. Both sets of knobs are "on" as far as I can tell. At least, they're not locked in either position.

My question: Where do I go from here? Not sure what kind of troubleshooting I can do.

Edit: It was the batteries. Hex screws, too. Could've sworn they were torx when I'd seen it.