There seems to be some confusion between “hops” and “repeaters” for a Z wave network, so let me see if I can clear up a couple of things.
A Hop is one leg of a message route
A “hop” refers to an individual transmission path segment of a message between two devices. this will normally be a message coming to or from the hub. Along the way, Z wave works as a kind of pony express relay system, where one device will carry the message as far as it can and then pass it along to another who will carry it as far as it can, and then eventually it will get to the destination.
Z wave has a hard limitation of four hops maximum Per message. That means if an end device is more than four hops from the hub, it becomes unavailable and messages can’t get through.
Typically each zwave device will have a transmission range of around 40 feet inside a typical US home, with Z wave plus going up to about 75 feet. But there are a lot of things that can reduce the distance the signal can successfully travel, such as brick, Adobe, cement, foil backed insulation or chicken wire lathing inside the wall, mirrors, fish tanks, Big metal objects like appliances or cars, water pipes, etc. Exterior walls are almost always more difficult to get signal through than interior walls. And metal doors can be extremely difficult to get signal through. Clear glass is usually OK, tinted glass can be a problem.
Sometimes two devices can be just 6 feet apart but not able to communicate because there is an 8 inch brick wall in between them.
Which Devices can repeat?
Most mains powered Z wave devices can repeat for other zwave devices on your network. The exception is usually smoke alarms: you don’t want a smoke sensor to wait to give an alarm because it’s busy passing along a message for some light switch somewhere.
Most battery powered Z wave devices do not repeat because it would use up too much battery life.
But there’s a catch…
That said, you want the repeater which is physically closest to a zwave lock to support “beaming.” This is an optional feature, so not all devices will do it.
Lock manufacturers have to meet two conflicting consumer demands. First, people don’t want to change the batteries In a lock more than once a year. Second, they want the lock to almost instantly respond when someone enters the code or runs an automation. (Basically, no one wants to be standing outside in the rain while they wait for the lock.)
OK, the normal way to extend battery life on a Z wave device is to make the device “sleepy,” that is, it is inactive most of the time and just wakes up periodically to see if anything is going on. But that doesn’t work for locks, because it would make the wait time Longer than people will tolerate.
So zwave came up with “beaming” which is A way to have a repeater which is close to the lock hold its messages and re-transmit them the instant that the lock wakes up. That’s very different than the pony express paradigm. Instead of just trying to get the message from one place to another as quickly as you can by passing it from rider to rider, when the message gets to the last stop before its destination, it is held there, and is soon as that station realizes the lock is awake, they tell them that they have a message waiting. And again, this was optional when it was introduced.
So for Locks, you want to always make sure that the repeater closest to the lock, ideally within 10 or 15 feet of it, supports beaming.
And to be honest it’s usually better If This repeater is not the hub, because the hub is always busy. Some random light switch sitting nearby may be better able to get messages to and from the lock very quickly because to be honest it doesn’t have that much else to do.
You can check the conformance statement on the official Z wave alliance product site to see if any specific model device supports beaming.
How many repeaters do you need?
First off, there’s no problem with having extra repeaters in a room. In fact it’s a good idea because it allows for alternate path if one repeater’s busy. Z wave is smart enough to figure out that if there are four repeaters in a room it shouldn’t use up all the hops on those four. It will always try to get the maximum distance out of each hop if it can. The algorithms for doing this Are really complicated, but you don’t have to worry about them. Just know that if you have two light switches and an in wall receptacle in one room, you’re not going to use up all your hops just because there is a choice of repeaters nearby. That’s basically the same as keeping multiple riders at one pony express station. It increases the options when messages come through but it doesn’t mean that the rider on a horse at station A is going to try to give the message to another horse right next to them. It just doesn’t work that way.
Best practices depends on the number of devices you have that need to use repeaters. If you have a room with 12 sensors in it I’d go ahead and put multiple repeaters there just to make sure they’re all not waiting in line for the same repeater to get the message out.
Just remember that for locks, the repeater which is closest to a lock will be designated to hold its messages when it is asleep. This is probably where somebody got the idea that you should have one repeater for each lock. It’s not really required, but it’s not going to hurt anything, and it may help keep messages from getting delayed-- but only if the repeaters support beaming.
If I understand what you’re describing, everybody walks in through the same main entrance and then they immediately see four doors with smart locks. One is the entrance to the basement apartment. One is the entrance to the main floor apartment ( where the hub is). One is the entrance to the common laundry room. And one is the entrance to the upstairs apartment. I’m assuming that each of these is built like an exterior door, so it may be harder to get signal through than a typical bedroom door.
So you have five smart locks that are quite close to each other. Most of them are two exterior doors away from the hub. And the main entrance door is one exterior door away from the hub.
None of these locks can repeat for each other: they are all battery operated devices. They’re all going to sleep part of the time. So you need a beaming repeater device to hold their messages, and usually it’s best if that’s not the hub.
You could probably do it with one in wall receptacle in the lobby area as long as it supports beaming, but you do run the risk that it could get overloaded with five doors to handle. There’s also the problem that people do tend to come and go at similar times, which means it’s more likely that the repeater will be busy when someone wants to open the door.
I’d be surprised if you needed five repeaters, but since this is a rental situation and you want your renters to be happy, I personally would probably use three.
Normally, putting a repeater inside one of the other apartments wouldn’t help you at all because the message would probably hit the lock before it hit the repeater. But again we run into that beaming situation. So it actually might help your network integrity to have a beaming repeater inside The living spaces, again just to hold the messages for the lock. It’s something you might just have to do trial and error with. But I would prefer to see them in the lobby area except for the one where the hub is.
So…there’s no problem having more than four repeaters, that does not affect in any negative way the The strength of the mesh. In fact it just makes the mesh stronger by giving each device more choices. Zwave is smart enough not to use the hops that it doesn’t need to.
But you need the repeater which is closest to each lock, or at least within about 10 feet of it, to be a beaming repeater. Zwave Locks have special requirements.
And while you don’t really need one dedicated repeater for each lock, I probably wouldn’t put three or four locks on the same repeater or the repeater might just get too busy to get the messages out in a timely fashion. I understand why @rboy might recommend one repeater Per lock: it makes his customer support issues simpler since messages are less likely to get lost. But for budget reasons I don’t think you need to go 1 to 1.
You do absolutely need to get repeaters that support beaming, though. Remember with the lock it isn’t just about distance, it’s about holding the message until the lock is awake and then transmitting it very quickly.
And you do need to run a Z wave repair once after you have installed all the repeaters or the locks won’t know they are there and they won’t use them, no matter how physically close they are. .