mmRadar has may uses and applications. This article outlines 20 uses for radar.
1. Tank level monitoring
A radar sensor could be placed on top of a tank or silo to measure the level of what is inside. One added benefit of radar is that it can see through walls, so if the tank is made of plastic, the radar can be placed on the outside without the need to drill holes.
2. Distance measuring
Radar can be used to measure distances very accurately. Unlike ultrasonic sensors, radar distance sensors are not easily affected by temperature, pressures and temperatures. Precisely measure the height of equipment off the ground, the distance between objects etc.
3. Speed cameras
Use the speed measuring capabilities of radar to create your own private speed camera (for use on private roads), just like the police.
4. Speed signs
Radar can be used to track the speed of vehicles, or anything else for that matter. Build your own personal speed sign using mmwave radar technology.
5. Radar gun
Want to measure the speed of a vehicle whizzing past (or anything else for that matter)? How about building your own custom radar gun?
6. Smart security cameras
Wish your security didn't trigger as the neighborhood cat walks past? Incorporate a radar sensor into a security light to sense between a person and the neighborhood cat.
7. Smarter security camera
Soup up a security camera. Go beyond simple motion detection to trigger security 'events'. By incorporating radar into the security camera, trigger only when a person or large object walks by.
8. Intelligent door sensor
Ever walk past an automatic door and have it open when you had no intention of going through it? Go beyond simple presence sensing. Radar can be used to determine the direction a person is walking and only open when a person is walking towards the door.
9. Occupancy detection
Use radar to detect if there is a person in a room is sitting in a specific spot. Radar can differentiate between moving and non-moving objects easily.
10. People counting
People have a particular radar 'signature'. Radar technology is a non-invasive way of counting people. No cameras - no privacy concerns. Radar can also see through walls and count people on the other side.
11. Collision Avoidance
Radar is used extensive in the automotive industry for collision avoidance. This same technology can also be employed on other smaller-scale robotics projects. Radar is much smarter than a simple ultrasound sensor. Detect the size, direction, and speed of obstacles.
12. Safety sensor for forklifts
Use a radar sensor to check for people walking behind equipment such as forklifts. Radar can be used to sense intelligently. People walking into the path of the forklift can trigger a warning while people walking away do not.
13. Blind spot detection
Modern cars use radar to assist with blind spot detection. For example, lights on wing mirrors light up when an obstacle is in the blind spot. This functionality is not limited to vehicles however.
14. Lane change assist
Similar to blind spot detection. "Lane change assist" technology used to identify obstacles moving beside/in parallel and is useful to prevent sideways collisions.
15. Search and rescue
Use Radar to detect movement in any environment. Radar sensors are robust and can be sent into hostile environments where humans dare not venture to look for signs of life.
16. Drone wire-crash prevention
Incorporate a radar sensor on a drone to detect unexpected obstacles in front of it such as power lines.
17. Backup vision sensor
Cameras are a brilliant tool for object detection and identification. They do have their limitations however. Cameras don't work well in low-light situation, can be easily be blinded by bright lights, don't work well in fog or smoky situations. Radar can be used as a backup-sensor in these cases. While radar doesn't possess the qualities of a camera, it is reliable when cameras are not, making it an ideal companion sensor. 
18. Confluence vision sensor
Cameras are a great tool for object detection and identification, however they can be tricked! Put a photo of a person in front of a camera and it will not be able to differentiate between that and a real person. Use a radar sensors to detect the 'signature' of obstacles and combine this information with the camera to increase the confidence of detentions.
19. Detect temporary obstacles in a 3D map.
Imagine creating an environment map of a scene for your robotics project using a lidar sensor. That is great, but how do you handle temporary obstacles such as people walking around? One of the benefits of radar is to be able to identify moving obstacles while rejecting static ones. This makes radar an ideal technology to incorporate into a robotics project which used an environment map.
20. Adaptive cruise control
Modern vehicles with adaptive cruise control make use of radar data to establish and maintain the distance to the vehicle in front of them. This technology can be used in a robotics project to enable the robot to both follow a target and maintain an acceptable distance.