PB-04Find the joists and check for hidden servicesRun a detector across the ceiling near your marked spot and look for a line of nail or screw heads in the plaster, which usually marks a joist. Before you drill anything, find your stopcock — usually under the kitchen sink — and check it turns, so you can shut off the water fast if you hit a pipe. Cables and pipes can run almost anywhere in a ceiling, and detectors miss ones that are deep, in conduit, or hidden behind old lath, so if there's any real doubt, isolate the circuit at the consumer unit before you drill.