I am hoping you may be able to help me out with a build. I have limited engineering experience with this type of project, but really am just looking for some high level ideas to point me in the right direction so I can really start researching areas or applicable technologies.
What I am looking to create is an alert system using the most affordable (from production cost standpoint), smallest, and accurate within range (let's say 30 ft) technology available. I would like to create two devices: 1) Device 1 that acts like a transmitter that can be carried very easily in a wallet or on a key chain and 2) Device 2 that can alert someone if Device 1 is within a nearby range, let's say within 30 feet. The alert on Device 2 can be an audible sound or small flashing of a light on the device itself. I would like Device 2 to also be as small and portable as possible (Eventually to be suctioned cupped to different surfaces).
I would like that both devices also be as efficient on power as possible. Battery is preferable for Device 1, and Device 2 should be able to be both battery operated or plugged into an AC Adapter or Car Charger.
Generally, the main direction I am looking for as of now is for ideas for what can be used for the proximity alert function--not sure if there is some RFID technology that would work or something similar.
Again, appreciate you reading this and lending some ideas.