Bluetooth beacon
Bluetooth beacon is what you are looking for.
Smart phones like iPhone and other Bluetooth devices such as iPod touch can detect the occasional signals emitted by these beacons.
Often these are used by the human to determine their location such as a shopper in a Home Depot or Target store for proximity marketing, or providing contextual information such as a visitor identifying artwork in front of them in a museum. In such a situation the beacon is attached to the shelves or walls and the smart phone scans for the occasional blips emitted.
In your situation, you may want the opposite strategy, as you seem to want the room to detect the presence of the humans. Have the humans wear the beacon and affix an iPod touch or some such device to the shelves or wall to detect each human passing by. For more than a few hours of detection, you'll need to have the iPod touch plugged in to a power supply.
There are a variety of vendors for this technology. For example, Estimote. This is a fast-changing field now, so I’ll not recommend any particular one. Plus you did not really provide enough criteria to make a recommendation amongst concerns such as price, size of hardware, color/aesthetics/fashion of the hardware, mode of attachment, battery life, technical support, type of software library, etc.
Those vendors provide libraries for triangulating a user’s position within a room containing multiple beacons. Sub-meter accuracy is possible.
Apple in particular has been a leader in this space, defining the iBeacon protocol and framework. Google followed, launching its Eddystone Bluetooth beacon system for Android in 2015.
