Two-Way Security Sensors Offer Convenience & Security

Two-way keyfobs from Elk Products and Z-Wave receive feedback from the alarm system, ensuring a message to arm or disarm has been received.


For years, security manufacturers have been building sensors with size, price and battery optimization as core principles.

Users don’t want to be changing batteries on a house full of sensors every year, especially when those devices are placed on ceilings and high up on the walls.

To that end, sensors have been built with RF protocols and communications schemes that minimize interactions. In the process, two-way feedback has been sacrificed in these one-way sensors, leaving the control panels to do the heavy lifting. 

For example, to determine if a sensor is still online, the panel listens for a ping from the sensors at select intervals. If those pings don’t arrive, then the alarm system knows something is amiss.

Ideally you would want the panel to be able to query the sensors to see if they’re online and doing OK, but that means the sensors would have to always be listening, which wastes batteries.

Elk Products

Thanks to new RF technologies and communications schemes, however, new two-way sensors for the home market have been available for the past few years from vendors like Elk Products, makers of the M1 family of security and home automation panels and peripherals.

Elk’s two-way capabilities are available on a diverse range of products including motion sensors (PIRs), smoke detectors and keyfobs. The company says the two-way nature of these products can actually save battery life because feedback can be obtained instantly, letting them know the message has been received.

“Conventional wireless transmitters ‘shout’ eight times, hoping to reach the receiver,” says Elk director of sales and marketing Trudy Philips. “However, Elk transmitters stop transmitting once transmission receipt is confirmed with an acknowledgement to the transmitter. This saves the battery power required for up to seven more transmissions traditionally sent by conventional wireless transmitters.”

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Two-way also translates into convenience and security. Let’s look at keyfobs, one of the great conveniences offered with most security systems.

Typically, users arm or disarm a system by pressing a button on the fob, but they have no idea if the message was actually received from the security system.

With two-way communications, products like keyfobs can receive a virtual thumbs up that a command was received. When a user presses the “arm” button, did the security system go into “arm” mode? If the red LED flashes, the house is indeed secured.

Elk adds another interesting feature that can only be implemented in two-way devices: an indication of alarm status. As the user approaches the home, a steady red light on the keyfob indicates the system is armed; a steady green indicates the system is disarmed; and a red flashing LED indicates the system has been compromised and it may not be safe to enter.


Earlier this year, UL approved the latest Z-Wave protocol for UL 1023 compliance, giving Z-Wave the green light for professional alarm installations, and mitigating consumer concerns about hacking the smart home.

Sigma Designs, the owner of Z-Wave technology, put the gears in motion last year when it launched the new Z-Wave Security 2 (S2) framework for next-gen Z-Wave products. That framework was developed in cooperation with UL, with 1023 compliance in mind.

Z-Wave’s two-way sensors feature “Jamming Detect,” a mechanism added to the protocol to satisfy UL’s stringent interference protection requirements.

So, in addition to their use as automation devices, the new Z-Wave sensors can be specified by professionals as life-safety products as well.