How to Play Multiplayer Games From Two Different Phones

The basic idea: one room, two devices

Cross-device multiplayer does not mean both people use the same screen. One player creates a room, the service stores the current match state, and the other player joins that room from their own browser. Both browsers listen for updates so each move can appear on the other device. A private room code is a short invitation that connects the players to the same match.

Step 1: sign in first

For CaveoAI’s online rooms, both people need to sign in. Authentication identifies which account is performing a room action. The site should not ask you to share your password with your friend; each player uses their own account on their own device. If Google sign-in does not open, check the browser’s pop-up permission and confirm that the site domain is authorised in the Firebase project.

Step 2: create and share a room

Choose a game marked Online Room, open the multiplayer hub, and press Create Room. The page shows a six-character code. Use the copy button or send the code through a private message. The second player opens the same game site, signs in, enters the code, and presses Join. Wait until the room status shows both player names before making a move.

If joining fails

Re-check the six characters and make sure both devices use the same public website URL, not one local development address and one live address. The site owner must enable Firebase Authentication, enable the chosen sign-in methods, create Cloud Firestore, publish the supplied rules, and add the site hostname to authorised domains. If a room cannot be read, the rules may not recognise the signed-in user as a participant.

Latency and fairness

A move might take a fraction of a second to appear because a mobile network must send it to the database and back. Avoid pressing multiple controls when the status says it is the opponent’s turn. A browser-based starter trusts the signed-in players’ client logic for some state transitions, so it should not be used for money, prizes, or high-stakes competitive rankings without server-side validation.

Protect your account

Room codes should be shared only with intended opponents. Do not include a phone number, school, address, or real name in a display name. Close the room screen when finished and sign out on any shared device. If you believe a room or account is being misused, leave it and contact the site owner with the room code and a short description—never your password.

Keep exploring

Try a related mode in the CaveoAI game library, and keep your sessions comfortable and balanced. For site questions or corrections, use our contact page.