Replace the batteries for your touch faucet if the indicator light on the faucet blinks continually. Depending on the brand, the battery pack is either inside the sink cabinet or the faucet spout. If the battery is inside the spout, there is a screw on the spout that requires a Phillips head screwdriver or hex wrench to remove to access the battery.
Clean the sensor on the faucet if it operates erratically. The sensor lens should be free of dirt and soap scum. Clean it with a damp cloth and wipe it dry with another cloth.
Check the wires that go to the faucet under the sink if the faucet does not work at all. Sometimes the wires may become disconnected if they were not installed correctly. Check each wire connector and ensure they are locked into each other snugly. Push any loose wire connectors together that have become disconnected.