Quantity   Component name
1 × SIM800L GSM module, the cheapest one is also the smallest
1 × Arduino pro mini, ATmega328P
1 × TP4056 USB-C charger Modified with 3K3 R3 resistor to limit charge current
1 × 0.91" 128x32 OLED display, I2C
1 × Speaker 1W 8 Ohm - 14 x 20 mm
1 × Electret microphone 6050
3 × Push button 6x6x10mm