Technician reported discovering 2 passenger O2 generators on a CRJ-900 still had safety pins installed on them that would have kept them from being activated.

Narrative

Maintenance techs were complying with RON package for aircraft. They were completing task card # XXXXXXXX under work order # XXXXXX. Upon removal of panels to access O2 generators they found safety pins that prohibit activation of O2 generators still installed.I was made aware of something this evening that I feel must be passed on to you. We had Aircraft X at the hangar tonight as a RON. Included in the package was task task card # XXXXXXXX; Verify Lanyard Alignment for O2 Generators. Aircraft was being worked on by Name 1; Name 2; and Name 3. When they removed the panel to gain access to the generators they found that several of the generators had the safety pin that prevents the generator from being activated still installed with a red safety flag attached. Two of these generators were located at the emergency exit doors. Had we not had this job card to perform this would not have been found. This aircraft was just released from Heavy Check today; and this was the very first flight after maintenance. I believe the event occurred due to complacency and failure to follow proper protocols after maintenance.Had this aircraft been carrying passengers and an actual emergency happened where these masks were needed several passengers would not have been able to receive any O2. I am not exactly sure who should also be notified to check into this or what else can be done so I am sending it to you. I just feel that this should be looked into further as this is a safety of flight issue to me. It makes me wonder what else might be getting missed or overlooked at this or other facilities like this one and how do we protect the company and our passengers from situations like this.