Nice idea, and you’ve got the right tools. Grab a cheap moisture sensor, a small relay to drive a tiny water pump, and hook it up to a Raspberry Pi. The Pi can run a simple Python script that logs moisture levels, triggers the relay when it drops below a threshold, and even sends you a text or pushes a notification. If you want that vibration, just attach a small motor to the Pi’s GPIO and activate it when the water pump starts. Repurposing an old phone is cool, but the Pi gives you a clean, low‑power platform and you can still keep the phone for the UI if you want a fancy touch‑screen later. Just remember to calibrate the sensor with a few trial runs—those little devices love to lie when you first plug them in. Good luck, and enjoy watching those herbs thrive while you keep a keen eye on every drop.