The WiFi code
This is the one every rental should have. Make it with the WiFi QR code generator, type the network name and password exactly, choose WPA2 unless your router is set to WPA3 only, and add the frame text "Scan to join WiFi". Print one copy for the welcome book and one for the wall near the router. The WiFi guide covers the details, including what to do when a code scans but does not connect.
Use a separate guest network if your router offers one, and remember that changing the password means printing a new code.
The house manual
Put the manual on a simple web page: heating, hot water, bins, appliances, parking, what to do if the power trips. Then make a website QR code for that page and put it inside the front door and in the welcome book. Because the code is static and the page is yours, you can update the manual any time without reprinting.
A code that opens a page beats a laminated sheet because you can add photos of the boiler switch, and guests can read it in their own language with their phone's translation.
Check-in and check-out
A code on the key box or by the door can open the check-in instructions, and one by the exit can open the check-out list: keys, bins, thermostat, windows. Keep these as separate pages so each code opens exactly what the guest needs at that moment.
Local tips and contact
A page with your favourite cafe, the nearest pharmacy and the bus stop gets used more than you would expect. A WhatsApp code with a pre-written "Hi, I am staying at ..." message gives guests a way to reach you that is quicker than the booking platform.
Placement and size
Codes in a rental are scanned up close, so 3 to 4 cm wide is enough. Put them at eye level where the question comes up: WiFi by the router and in the living room, the manual by the door, appliance codes on the appliance. Use plain card or matte laminate; gloss reflects the ceiling lights.
Keeping codes working
Static codes do not expire, so the only things that break them are a changed WiFi password or a moved page. Keep the page addresses fixed, and put a note in your changeover checklist to reprint the WiFi code whenever the password changes.