Yes, you can use your smartphone as a fish finder by pairing it with portable, castable wireless sonar devices manufactured by companies like Deeper or Garmin. These compact, ball-shaped sonar units float on the water or drop directly down an ice fishing hole, transmitting real-time bathymetric data, water temperature, bottom contour, and fish location metrics via Bluetooth or Wi-Fi to a dedicated application running on your iOS or Android smartphone screen.