The NBIoT manhole detection sensor can be installed on the bottom of different manholes with high protection IP67 enclosure. It is designed with ARM32 bit low power CPU with position detection and ultrasonic liquid sensor. It is powered by 8000mAh Lithium battery which can last for 3 years under 4 times uplink per day. The Manhole sensor can send real time status of the manhole such as manhole angel and water level to cloud server like ThingsMaster OTA through NBIoT B1/3/5/8/20/28 band. The manhole sensor can be applied for many smart city projects to enhance public safety.