Per John Niyo, cornerback Kevin Hobbs has received only the right of first refusal tender, which is the lowest tender that can be extended. Since Hobbs came into the league as an undrafted rookie, this tender means that if another team wants to sign him, the Lions will simply get the right to match the offer. If the offer is not matched, then Hobbs will leave for a new team and the Lions will not get anything in return.
This scenario played out a couple years ago when Kalvin Pearson joined the team. He was a restricted free agent for the Buccaneers and the Lions signed him to an offer sheet. Tampa Bay decided not to match the offer, but since he was originally undrafted and had the lowest possible tender, the Bucs didn't get any compensation for losing him to Detroit.