A portable table number device, comprising a housing having a bottom side with an outer edge arranged to rest on a table surface, said housing comprising a power source, an RFID reader arranged to detect an RFID table ID tag on or under said table surface, computer memory means comprising a table number device ID, wireless communication means arranged to wirelessly communicate a detected RFID tag table ID by said RFID reader together with said table number device ID to an external table number receiving device, a surface proximity sensor, such as a light sensor or micro-switch arranged in a recessed portion of said housing within said outer edge, said surface proximity sensor having a first state wherein no proximate surface is detected and a second state wherein a proximate surface is detected, said second state occurring if said bottom side of said housing is placed on said table surface, and power management means arranged to keep said RFID reading device in a sleep mode wherein no or relatively little power is used until the state of said surface proximity sensor changes from said first state to said second state, to power up said RFID reader temporarily for a period of time if the state of said proximity sensor changes from said first state to said second state, said period of time being long enough to enable said RFID reader to identify an RFID tag and transmit it to said external table number receiving device, and to put said RFID reader in said sleep mode after said period of time lapses.