There are a few ways to tell if someone has a burner phone. One way is to look for an unfamiliar phone number. If the number is not in your contacts and you don't recognize the area code, it's likely that the person is using a burner phone. Another way to tell is by looking for multiple SIM cards. Most burner phones only have one SIM card, while regular phones have two or more. Finally, you can ask the person if they're using a burner phone.