Zigbee devices can transmit data over long distances by passing data through a mesh network of intermediate devices to reach more distant devices.
On the other hand, Wi-Fi works on a Star topology network where each individual device is directly connected to a central router. This manner of attachment can be visually represented in a form similar to a star.
Both Zigbee and Wi-Fi operate in the 2.4GHz bandwidth. However, the ZigBee Alliance understood that it’s a busy channel, so they took steps to ensure that their products would work without causing or being affected by interference. ZigBee products can detect collisions and will retry transmissions multiple times. Third party testers found that ZigBee networks have little-to-no impact on Wi-Fi since ZigBee packets are tiny and brief.
On the other hand, Wi-Fi smart devices are connected directly to your router access point.
You might have experienced your internet speed slowing down when the multiple smart phones, laptops, smart TVs connected to your Wi-Fi router are in use at the same time. I guess you can figure out what happens when an additional 10-15 Wi-Fi smart home appliances are added to this network.
Most Wi-Fi networks are secured by a type of encryption called WPA2. At this time, the main vulnerability of a WPA2 system is when an attacker gets their hands on your SSID (the unique ID of your secured wireless network) and Wi-Fi password. These can be used to perform attacks on your other connected devices.
So here comes the major problem… When you connect Wi-Fi smart home devices to your network, you effectively surrender your SSID and password to multiple vendors. Where do they store this information? How well do they store it? That is a big question mark. Is that a risk you are willing to take?
On the other hand, the Zigbee protocol has an additional layer of robust encryption. This further strengthens the communication between the Smart Hub and Zigbee smart devices. When you are connecting a new Zigbee device to the smart hub, you do not need to give away your Wi-Fi SSID and password.
The Zigbee Alliance and its members take security very seriously. Standards and protocols are developed to strike the right balance between ease of use and secure interaction of devices to offer smart functionality with essential security measures in place. Zigbee technology is created and implemented by many of the most successful companies in the world, all of which have access to the latest security schemes. Members of Zigbee Alliance technical working groups actively review the Zigbee security framework as well as industry best practices.
Your Zigbee smart devices will still work even if your internet is down. This is possible because the Zigbee communication is independent from the Wi-Fi.
Hence quick control buttons such as “I am leaving home – to turn off all electronic devices” or automation rules such as “When motion detected in walk-in wardrobe, lights turn on” will still work!
In contrast, for Wi-Fi smart devices, if your internet is down, all your Wi-Fi smart devices will no longer be able to perform its “Smart” functions.
 Carroll, B. (2018, August 10). Zigbee Leads the Wireless Mesh Sensor Network Market. Retrieved from https://zigbee.org/zigbee-leads-the-wireless-mesh-sensor-network-market/
 Skøien, K. R. (2018, December 27). Wireless Network Topologies. Retrieved from https://blog.nordicsemi.com/getconnected/wireless-network-topologies
 Carroll, B. (2016, November 8). Zigbee Alliance Statement on Security. Retrieved from https://zigbee.org/zigbee-alliance-statement-on-security/