When you need to handle input from multiple devices (e.g., two keyboards or a keyboard and a mouse), you can't block on one device's poll() — the other device's events would be delayed.

Polling multiple devices manually

Create a selector to manage multiple devices:

local evdev = require "evdev"
local Device = evdev.device.open
local Selector = evdev.selector.new

local kb  = assert(Device("/dev/input/event1"))
local mouse = assert(Device("/dev/input/event3"))
local sel = Selector({ kb, mouse })

while true do
  local ready = assert(sel:poll())
  for _, dev in ipairs(ready) do
    local e = dev:read()
    if e then
      local source = (dev == kb) and "keyboard" or "mouse"
      print(source, e.type, e.code, e.value)
    end
  end
end

sel:poll() waits until at least one registered device has data and returns the subset that are ready.

The events() iterator

For convenience, sel:events() yields (device, event) pairs:

for dev, e in sel:events() do
  if evdev.events.is_key(e) then
    print(dev.name, "key:", e.code)
  end

  if evdev.events.is_rel(e) then
    print(dev.name, "mouse moved")
  end
end

The iterator polls all devices until at least one has data, reads from each ready device, and repeats when drained.