Smart Bathrooms Built on Radar

By Edmund Cher

Program Manager

December 23, 2019


Smart Bathrooms Built on Radar

There are many sensors that can be used in a smart bathroom for data acquisition and control, but all of them make 'sense.' Radar is sensitive enough for advanced gesture recognition applications.

You walk into the bathroom. Your favorite music station is already playing and the mirror is synchronized with your smartphone, showing your daily appointments, current weather conditions, and traffic information. You move closer to the mirror and light along the edges of the mirror automatically brightens to provide a more detailed view of your reflection.

Smart device technology is everywhere today, and it has now migrated to the bathroom. A “smart bathroom” can offer new, more convenient ways to use faucets, showers, toilets, lighting and mirrors – all while helping conserve water and energy.

But what sensors can be used in a smart bathroom?

Smart Bathroom Sensing Options

While there are many possible sensors that can be used in a smart bathroom for sensing, command, and control, but all of them make "sense." For instance.

  • Camera technology cannot be used for obvious security and privacy reasons. Most smart bathrooms instead opt for voice recognition, smartphone connectivity, and motion sensors.
  • Passive infrared technology is a popular choice for many motion sensing applications. But in a smart bathroom, where appliances and fixtures must turn on immediately when a human is detected, passive IR sensors are not suitable because a significant amount of movement is needed to trigger them.

By comparison, radar technology is sensitive enough to detect smaller, more subtle movements like finger gesturing, breathing, a raised hand for hair brushing or even the twitch of a nose. Radar sensors, unlike current PIR sensor technology, are also not susceptible to condensation and water stain build up, reducing the amount of cleaning and care required.

The 24 GHz band is one of several internationally-recognized, license-free frequency bands that is suitable for radar-based motion sensing. At 24 GHz, the wavelength and size of a radar is small enough to be easily integrated into a variety of devices. These sensors also use very little power.

Video 1. 24 GHz radar sensors are accurate, small, and low-power enough to be deployed in smart bathroom applications.

For example, Socionext’s SC1232AR3 24 GHz CMOS radar sensor measures in at 9mm x 9mm x 1.18mm and runs at an average of 0.5 mW power. The SC1232AR3 comes with two integrated 2 RX antennas that support 1D motion and distance detection.

Figure 1. Socionext’s SC1232AR3 24 GHz CMOS radar sensors support 1D motion and distance detection.

These characteristics, along with a price point of $15 per qty. 100, make it suitable for use in battery-powered devices. Figures 2 and 3 show how the device can be deployed in the context of a smart bathroom.

Figure 2. Radar sensors such as the Socionext SC1232AR3 are capable of precision motion detection for applications that rely on entry detection (or entry into a given detectable area) or general human presence detection that requires continuous sensing in a given region.
Figure 3. Radar sensors can also detect distance and be used for path planning (approaching, loitering, departing) to enable pre-programmed routines such as playing music from specific radio stations, displaying weather forecasts, communicating traffic conditions, and providing daily appointment reminders.

The following illustrates how radar motion detectors can be used to control various “smart” functions inside a bathroom.

Increased Reliability for General Sensing

Smart fixtures such as a faucet, shower, light and toilet can also function as standalone units without integrating into any unified control console such as the smart mirror. These fixtures are ideal for on/off water control and temperature adjustment.

The picture in the left shows a smart faucet with presence and distance detection. which allows for the on/off control of the water flow. In addition to presence detection for turning water on/off, gesture control allows for water temperature adjustment and control of the water capacity for toilet flushing.

Towards Advanced Gesture Detection, Recognition, and Control

Utilizing radar sensing technology, next-generation smart mirrors will have built-in gesture recognition and 3D proximity sensing. The below diagram illustrates how a smart bathroom device can use the Socionext SC1232AR3 24GHZ radar sensor to detect distance.

Figure 4. Radar sensors can be used to detect not only distance, but also three-dimensional motion for gesture recognition.

However, in order to transform an everyday object like a smart mirror into a centralized bathroom control console, more advanced sensing may be required. For instance, touchless control such as screen scrolling, station tuning, volume adjustment, and remote faucet and shower management require a sensor devices that can detect gestures in three dimensions.

This level of gesture control is available through devices like the Socionext SC1220AT2, a 60 GHZ sensor. This more avanced radar sensor comes with 2 TX and 4 RX channels that enable gesture detection across X, Y, and Z axis.

As an individual enters within a certain range of the sensor, a gesture-aware algorithm is enabled that can recognize a range of hand gestures used to control a smart bathroom.


The smart bathroom of the future is also easy to integrate in today’s households. By utilizing existing Wi-Fi networks, users can add a variety smart devices and fixtures that help save water and energy, provide greater convenience, assist in our daily routines.

Still, these applications will not take off if the enabling technologies do not meet certain requirements. They must be accurate, reliable, and avoid any potential invasion of privacy and security.

Compared to cameras and PIR sensors, radar offers a solution that is unimpeded by environmental conditions, anonymous to the user, and ideal for touchless gesture recognition and control.


Edmund Cher is a Program Manager of IC Development at Socionext America Inc. Edmund has background in Electrical Engineering and has extensive industry experience in ASIC design and program management.


I focus on exceeding expectations in delivering $5M+ programs, watching the details from concept to production. I apply my expertise in consultative decision making, based on risk assessment and mitigation, in ensuring executive team approval of my strategic efforts. As a skilled negotiator, I look to find cost-effective win-win opportunities that drive the business.

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