1. Input voltage range: 5V–18V DC. 2. Self-ejecting SIM card slot supports standard mini-SIM cards. The module automatically powers on and connects to the network upon power application, eliminating manual activation. 3. User-controlled power on/off functionality. Direct startup upon power-up; includes a reserved power-on pin. 4. Built-in TTL level conversion circuitry ensures compatibility with common microcontroller serial interfaces—no external level shifter required. 5. Audio interface with dedicated pins for headphone and microphone connections. 6. Supports TTS (Text-to-Speech) and DTMF (Dual-Tone Multi-Frequency) functions for voice playback and keypad signal detection during calls. 7. Bluetooth 3.0 compliant with enhanced antenna design for improved signal performance; supports SPP (Serial Port Profile) and audio streaming. 8. Reserved BAT port for external lithium battery power supply (e.g., 3.7V Li-ion or 18650 cell—not included). 9. Multiple antenna interface options: D-type connector, SMA connector, and spring antenna connector. 10. Status LED indicator: Flashes once per second when no network is detected, no SIM is present, or SIM is improperly inserted; flashes once every three seconds when successfully connected to the network. 11. Color: As shown in product images. 12. Material: Plastic + metal. 13. Package contents:   1 × Development board   2 × Pin headers   1 × Antenna   Note: No other accessories included. 14. Note: Screen/display variations and lighting conditions may cause slight color differences between images and physical product. Dimensional tolerance: ±1–3 cm.