Is this device a repeater?
Original article written by @JDRoberts on the following page: https://community.smartthings.com/t/faq-is-this-device-a-repeater/25626
So you've read a little about range and message repeating, and you suspect that the reason why there's this huge lag in a lightswitch going on in your bedroom, or why you're having problems with your lock, is because your devices are out of range.
Adding a second hub won't help under the current architecture, whether it's V1 or V2.
To extend the mesh, you need more devices capable of "repeating" the specific messages you want repeated. That's so they can do their little relay thing of passing the message along like a old-fashioned horseback messengers. Ride till your horse gets tired (end of your range), pass the message onto the next guy who then rides as far as he can and so on until the message reaches its destination.
Which devices don't repeat?
Most battery-powered devices do not repeat, no matter what their protocol is, because it would use up their batteries too fast.
Most life-and-death emergency alert devices, like hardwired smoke detectors, do not repeat because there's too much danger that they might miss one of their primary mission alerts while they were repeating a message for some lightbulbs somewhere.
Wired "auxiliary" switches that don't have a radio can't repeat. They're really just wired remotes for their Master switch. So if you buy an "add on" or "auxiliary" switch that has to be wired directly to a Master, it probably doesn't repeat. If it communicates with the Master wirelessly, it may repeat if it is itself a certified Z-Wave/ZigBee device.
Sengled zigbee bulbs are unusual in that they do not repeat for anything, not even other bulbs.
Other than that, when it comes to ZigBee and Z-Wave, most mains-powered devices repeat for their own protocol. So if it plugs in or is hardwired, and it's not a smoke alarm, it probably repeats.
With the newest protocols, you don't need dedicated repeaters. Just let a light switch or plug in module do double duty.
The devices most commonly used as repeaters are light switches and plug in modules. That's because you get double duty out of them, you can use them in most rooms and they're not very busy anyway. Lights which might be used, what, six or seven times a day? In between it might as will repeat for other devices.
With the most current generation of Z-Wave and ZigBee it is unlikely that you need a dedicated range extender or signal booster. Just an ordinary switch that is capable of repeating is enough.
You have multiple networks in your home, each carrying its own messages:
1) Z-Wave mains-powered devices and Z-Wave light bulbs repeat Z-Wave messages. Just be aware that Z-Wave only allows up to four "hops" in a communication chain so you need to be able to reach your destination in four hops. But the devices are smart enough to pick their own routes, they will go for the neighbor at the farthest end of the range If needed. You could have seven light switches in the living room, and the message will still only take one hop to get across that room and then go on to another repeater in the hallway.
2) Special case: Z-Wave battery-operated locks. Z-Wave battery-operated door locks do not repeat for others. And they have a special rule for receiving their own messages. If you want to send messages to them, the last device in the sequence must support "beaming". This is a special Z-Wave feature which will cause the repeater device to keep sending its message several times, just in case the lock was asleep the first time the message came by. This is intended to improve response time for locks.
If you have a zwave lock which is on your network, but the status always seems to be wrong, you probably need to add a beaming repeater within about 15 feet of that lock. The other devices in the chain do not need to be beaming, only the very last one since it's the only one that will repeat the message for the lock
3) ZigBee Home Automation mains-powered devices repeat ZHA messages. They do not repeat most ZigBee light bulb messages.
4) Special case: ZigBee lighting, including the Hue Bridge. ZigBee Light Link (ZLL) mains-powered devices and some ZigBee light bulbs repeat ZLL messages. They do not repeat most ZigBee Home Automation (ZHA) messages. Any bulb connected to the Hue Bridge will form a mini network with it and only repeat messages for other devices connected to that bridge.
So if you have a plug-in module (or a light switch) that is Z-Wave, it can repeat a message for A Z-Wave lightbulb, a Z-Wave light switch, another plug in module, and a Z-Wave battery operated sensor. It can repeat a message for a Z-Wave lock, but it can only be the last step in the communication chain to the lock if it also supports beaming or the lock may not get the messages.
If you have a plug-in module that is ZigBee it can repeat a message for a ZigBee light switch that uses the ZHA profile, another plug in module, a ZigBee battery operated sensor, and a ZigBee lock. It cannot repeat messages for most ZigBee lightbulbs, because they use a different protocol, ZLL. It also cannot repeat for a Hue Bridge.
If you have a ZigBee lightbulb connected to a Hue Bridge, it can only repeat for the other devices also connected to that same Hue bridge. They basically form their own little mini network, using ZLL.
If you have your hub in your garage, then five light switches in your living room, five Z-Wave battery-operated motion sensors in your hallway and five more Z-Wave light switches in the master bedroom at the far end of that hallway, the mesh might be very weak because the motion sensors will not repeat for the light switches. So your signal might get from the hub to your living room and then just stop there. It doesn't get all the way to the master bedroom.
If you had the same house layout, but with only one light switch in the living room, one Z-Wave light switch in the hallway, a motion detector and one Z-Wave light switch in the bedroom, then everything might be working great because the light switches can pass the messages on down the hallway in both directions.
This is why it's not just the type of devices you have, but where they are that determines the strength of the mesh.
It's also why you need to do a Z-Wave repair once all the devices are in place. If you originally paired your motion sensor right next to the hub, then took it to the bedroom, it may actually not know that the hall way switch is one of its neighbors. So they won't ask it to relay messages. That can be a problem. Network repair takes care of this by making every device update who its true neighbors are, thus improving message repeating the next time around
Hops and Distance
The maximum distance a single device can transmit is called a "hop." The signal is omnidirectional and travels 360°. This distance can be affected by architectural features like brick walls, foilbacked insulation, metallic wallpaper, concrete floors, etc. In a typical US house, zigbee will transmit about 40 feet in a single hop and zwave plus will transmit for 60. However, zwave plus is limited to four hops per message while Zigbee can go 30 (15 into the hub and 15 out again.)
The following topic discusses more about range and repeaters:
There are examples of specific devices that can work as repeaters: