SIGNL4 is described as 'Mobile-app-based alerting service. It provides persistent, traceable mobile notifications and reliably routes critical alerts, incidents and events to staff on duty. It directly links operations teams with critical IT, OT and IoT systems' and is an app. There are more than 10 alternatives to SIGNL4 for a variety of platforms, including Web-based, Android, iPhone, iPad and SaaS apps. The best SIGNL4 alternative is Pushover. It's not free, so if you're looking for a free alternative, you could try Notify.Events or OpenDuty. Other great apps like SIGNL4 are TaskCall, OpsGenie, PagerDuty and xMatters.