Short range battery operated 2 part (door alarm type) distance sensor.

Hello all! I'm looking to design a range compact distance sensor that will sense 1-4 ft increments. If necessary i could modify a door alarm. id like to fab one or multiple if need be to sense the distances noted. I could utilize a buzzer or some way to record a voice that would alert to said distance. The battery voltage max is 4.2v dc and if it could be rechargeable that would be a plus. Any help on this would be greatly appreciated. Thanks!

Arduino, ultrasonic or laser sensors, sound module, speaker and the required code....
I would start n the Arduino playground with the many examples for the basic components, then combine what is needed and fill in the missing code bits.

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