Inclusion Criteria:  Veterans eligible to receive care by a VA provider History of at least one deployment in support of Operation Enduring Freedom (OEF), Operation Iraqi Freedom (OIF), and Operation New Dawn (OND) Current diagnosis of PTSD per the Clinician Administered PTSD Scale-5 (CAPS-5) Willingness to wear the Apollo daily and to comply with study protocol Android or Apple smart phone on which the participant can download the Apollo mobile app Age between 18 and 65 Ability to provide informed consent  Exclusion Criteria:  Inability to adequately respond to questions regarding the informed consent procedure Currently involved in the criminal justice system as a prisoner or ward of the state Current (past month) alcohol or substance abuse or dependence Lifetime history of bipolar disorder, psychosis, or delusional disorders Lifetime history of oppositional defiant disorder or anti-social personality disorder Pregnancy Recent medication changes in the past 4 weeks A current beta blocker prescription (other than prazosin) Active untreated visual impairment