What’s new in sensors for smart homes: part 2

As noted in Part 1, some of the latest offerings for smart home sensors are based on sensor integration, technology, and connectivity. However, identified needs have created new applications that were not possible, simply not considered, or only offered for businesses — until recently.

For example, the smart shelf was offered to retailers over 20 years ago. More recently, thanks to cloud technology, Amazon has offered the Dash smart shelf that provides an auto-replenishment scale for home and business use. With a consistent product stored on the shelf, when a low inventory level is reached, the scale triggers a purchase that can be fulfilled without user involvement. In a commercial environment, sensors could include RFID and optical sensors. For home use, however, the scale simply weighs items using load cells or other weight-sensing technologies.

Figure 1. The smart shelf can indicate when a product reaches a level and automatically reorder it for the user (Image: Amazon).

Mailbox sensor

One smart home sensor that is quite intriguing is a “you have mail” sensor for your physical mailbox. The outdoor wi-fi-based motion sensor informs the user when mail is delivered, or the mailbox is tampered with. A longer-range antenna can receive the signal as much as 100 feet away from a remote mailbox. Other functions can be triggered with appropriate network apps once the mailbox sensor detects/triggers the alert through an appropriate app. For some implementations, a bridge may be required to connect to the wi-fi network.

Water leak sensor

A leak detector can avoid serious damage from an undetected water fault from a hot water heater or water pipes. With the leak detector flat on the floor, the distance between the probe and the floor is about 1 mm. When water leakage exceeds this level, the probe touches the water and alerts the user.

The technology in a leak detector could be a bimetal sensor that expands at different rates. Based on the expansion characteristics of the two metals when exposed to water, it closes a set of contacts similar to a thermostat. Alternatively, a leak detector could use conductivity sensing, where two or more metal prongs act as electrodes. Electricity flows between the electrodes when moisture escapes from a leak and pools in an area. It activates audible and/or visual alerts and may also be monitored by an app.

Other leak-sensing technologies could include sensitive, built-in microphones to hear dripping water or a dampness/humidity sensor to detect high moisture levels and detect the leak before water accumulation occurs.

Wind speed sensor

While “you don’t need a weatherman to know which way the wind blows,” some people may want to know the wind speed and direction, be able to monitor it remotely, and possibly activate something based on the wind speed. Manufacturers have solved this problem and offer sensors that determine wind speed and direction using ultrasonic technology. The sensors measure the time between when a signal is sent and received in two different locations. Since the wind’s acceleration affects the time between the two readings, the comparison allows for calculating the wind direction.

The smart home environment

Most smart home sensors are used indoors in a temperature-controlled, benign – not harsh – environment. Consequently, special ratings and qualifications necessary for commercial, industrial, or automotive usage are not required. This allows them to be very cost-competitive – the key to increased usage in smart homes.