Sub carrying tourists to Titanic is missing

BBC News - Titanic tourist submersible goes missing with search under way

Updated article, including details about the sub. Looks like they could have at least 3 days of oxygen.
 
Read "The missing Titanic tourist submersible was piloted with a video-game controller, had a water bottle for a toilet, and previously got lost for 2 ½ hours on a CBS TV segment" on SmartNews: The missing Titanic tourist submersible was piloted with a video-game controller, had a water bottle for a toilet, and previously got lost for 2 ½ hours on a CBS TV segment (Insider)

Interesting background and historical information on the missing submersible. Sounds kinda low tech.

I find it hard to believe the craft has no independently powered distress/locator beacon. Some sort of electronic "pinger" similar to what we put on aircraft flight data recorders to aid in their recovery.
I'd think there's a far great chance a distressed craft like this would more likely to be heard than visually sighted or detected with magnetic anomaly detection gear.