To turn on Galaxy S21, press and hold the Side key until the Samsung logo appears on the screen. This is the primary meaning of "opening" your device, powering it on for the first time or after a factory reset, rather than physically disassembling the hardware, which the Galaxy S21 is not designed for.
What 'opening' your Galaxy S21 really means
When searching for how to open a Galaxy S21, most people actually want to turn on the phone and set it up for the first time, including inserting a SIM card. A smaller number may be looking to physically open the device for repairs, but the Galaxy S21 has a sealed design and is not user-serviceable for internal components like the battery or storage. If you need to access the SIM card tray, that is the only external access point, and instructions are provided below. AT&T's article covers model codes SM-G991U / SM-G996U / SM-G988U. Verizon's support overview groups Galaxy S21 5G / S21+ 5G / S21 Ultra 5G together for activation and setup help. Samsung's manual is for Galaxy S21|S21+|S21 Ultra 5G G991.
How to turn on your Galaxy S21 for the first time
- Press and hold the Side key (located on the right edge of the phone) until the Samsung logo appears on the screen.
- Release the Side key once the logo displays. The initial boot may take a moment as the phone prepares for first-time use.
- If the phone does not respond, connect the charger to the phone and wall socket, then press and hold the Side key until the phone turns on.
Following the on-screen setup wizard
After turning on your Galaxy S21 for the first time (or after a factory reset), the Setup Wizard begins automatically. The AT&T setup flow specifies the phone prompts for language, then Start, then Details for terms and privacy items before Wi‑Fi and account sign-in. Setup flow varies slightly by carrier page: AT&T documents Start and Details button labels, while Samsung's manual gives broader Setup Wizard prompts without those exact button names. This guides you through essential choices: selecting a default language, connecting to a Wi-Fi network, reviewing terms and conditions (tap Details to read privacy and diagnostic data items), and signing in with a Google account using your email or phone number. You will also be prompted to set up location services and learn about device features. If you need help activating phones and SIM cards on any carrier, the wizard includes steps for verifying your SIM and network connection.
What to do if you need to insert a SIM card
- Locate the SIM card tray on the top edge of the Galaxy S21.
- Insert the SIM eject tool (included in the box) into the small hole on the tray to pop it out.
- Place the SIM card into the tray with the gold contacts facing down, then reinsert the tray firmly.
- If prompted for a SIM PIN, O2 states the default SIM PIN is 0000. Enter it and press OK.
Troubleshooting: when the phone won't turn on
If your Galaxy S21 does not respond when you press the Side key, first connect it to a charger and let it charge for at least 15-30 minutes. A completely drained battery may need time before the phone can power on. If the device still shows no sign of life, you may need to perform a hard reset, refer to the separate guide on factory resetting your Galaxy S21 for those steps.
Frequently Asked Questions
Can I open the Galaxy S21 to replace the battery?
No. The Galaxy S21 has a sealed battery that is not user-replaceable. If you experience battery issues, contact a certified technician or visit an authorized service center.
Can I open the Galaxy S21 to upgrade the storage?
No. The internal storage is not expandable through hardware upgrades. You can use cloud storage or an external USB‑C drive for additional space.
What should I do before opening the SIM card tray?
Ensure the device is powered off before inserting or removing the SIM card. It is also a good practice to back up important data, though this is not required for SIM tray access.
Is it safe to clean the internal components of the Galaxy S21?
No. Opening the device to clean internal parts is not recommended. Use compressed air to gently remove dust from external openings like the charging port or speaker grills.
