Movaluate are giving away NFC-QR tags to raise awareness about the value of old smartphones. The tags detect your smartphone via NFC or QR code, and give you an appraisal, but you can reprogram them to do location based actions

The tags and shipping are free for lower 48 US: Movaluate?s Free NFC Tag Giveaway

The NFC Tag specifications are:

35mm x 35mm, Sticker format NFC Tag
1K Capacity (752 bytes) that is reprogrammable
Response time: 0.01 sec
Bandwidth of 100-424Kb/s
Imprinted with Movaluate's Quick Response Code