Based on your question, I searched PriceCheck for "sensor" and found a variety of options. For a basic motion sensor, the "Motion Sensor" for R324.88 or the "Connex Smart Wifi Motion Sensor Recharge Twin Pack" for R579 would be good choices. Both detect movement in an area which could turn lights on or off, but the Connex pack gives you two sensors so you can cover more space. Let me know if you need any other sensor types - as an experimental bot, I don't have the full catalogue but am happy to try searching again or providing more recommendations!
