The goal of this study is to test the effects of just-in-time intervention strategies aimed to promote implementation of the safety plan and its components at different levels of suicidal urges and intent. The main questions the investigators aim to answer are:

1. What is the acceptability and feasibility of the just-in-time intervention strategies?
2. What are the proximal effects of just-in-time intervention strategies aimed to promote use of the safety plan and its components?
3. What internal and external contextual factors moderate the just-in-time intervention effects?

Participants (adults hospitalized for suicidal thoughts or behaviors) will:

• Answer questions about current suicidal thoughts on their smartphone up to 4 times each day during both hospitalization and the 4 weeks after they leave the hospital
• Each time they submit a survey, be immediately randomized to receive (or not receive) a just-in-time intervention tailored to their level of current suicidal thoughts
• Answer brief follow-up questions on their smartphone within a couple hours of each randomization
• Provide feedback on their experience with the just-in-time interventions

As the 12th leading cause of death in the United States, suicide is an alarmingly prevalent public health problem. The time period of highest risk for suicide and related behavior (SRB) is immediately (e.g., the weeks) following psychiatric hospitalization. Effective and scalable strategies for preventing SRB among individuals recently discharged from inpatient treatment are urgently needed. Encouragingly, brief evidence-based interventions now exist that reduce risk for suicide after acute psychiatric care. A primary example is safety planning, which involves developing a prioritized list of coping strategies and sources of support that people can use to mitigate future suicidal crises; this intervention is now recommended as part of standard inpatient clinical care. However, it has been shown that well over one-third of suicidal patients who have a safety plan never use it. Additionally, little is known about when (and for whom) specific components of the safety plan, which includes internal coping strategies, social support activities, and help-seeking behaviors, are most accessible and effective. Optimizing real-world safety plan use with scalable intervention strategies delivered via mobile technology has great potential to improve the effectiveness of an already promising intervention and advance precision treatment for high-risk individuals.

This project will employ the recently developed micro-randomized trial (MRT) design to test the effectiveness of brief, just-in-time interventions aimed to promote real-world use of the safety plan and its specific components. Both the method (e.g., phone call or text messaging by a human or automated forms of smartphone-based messaging) and content (e.g., recommendation to use the safety plan in its entirety or a specific component) will be randomized according to individuals' current levels of suicidal urges and intent. Participants will be psychiatric inpatients admitted for suicidal thoughts or behaviors who agree to participate in an intensive longitudinal monitoring protocol involving real-time smartphone-based surveys for the 28 days after hospitalization; after each completed survey, participants will be repeatedly "micro-randomized" to one of several just-in-time interventions. The investigators will test the hypotheses that the brief just-in-time interventions will be both acceptable and feasible, and associated with increased use of safety plan components (target mechanism) and reductions in suicidal thoughts (proximal outcome) at varying levels of suicidal thoughts, and that intervention effects will vary by both intervention method and content. The investigators will also explore internal and external contextual moderators (e.g., affect, social support) of proximal intervention effects, and collect qualitative data that will inform intervention refinement as well as the future development and implementation of just-in-time adaptive interventions.

The investigators will first conduct a small pilot MRT (N=10 participants), after which qualitative feedback collected on the intervention methods, content, amount of support, timing, and triggering, as well as overall data on acceptability and feasibility, will be used to refine the interventions before the full MRT (per Question #1 outlined above). The full MRT of the refined just-in-time interventions will be conducted in N=175 participants (and answer Questions #2 and #3 above).

Inclusion Criteria:

• Experiencing suicidal thoughts as part of their inpatient admission
• Access to a smartphone following discharge
• Ability to speak and write English fluently

Exclusion Criteria:

• Any factor that impairs the ability to effectively participate in the study (e.g., significant cognitive impairment, intellectual disability, presence of violent behavior, psychotic illness/symptoms determined by the treating clinician to impair ability to understand the study or provide informed consent)
• Failure to correctly answer all true/false questions in the consent form