Used a nRF24L01, SSD1306 OLED. Locally transmits to rPi machine which sends an MQTT message to a cloud server that posts to APN. Entire trip takes ~300ms. An iPhone app allows you to respond with a message, "come back later, please leave package, be right there." Used a 3d printer to create the enclosure that measures 4 x 4 x 8 cm. Powered by a single 3.7 lipo, uses a solid state switch to turn off after 120s.
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