Here are three of the most effective Home Security Systems used today:
With SimpliSafe you get 24/7 live monitoring, a cellular connection for Simplify devices, environmental monitoring, the ability to activate the system from anywhere, smartphone alerts, video alarm verification, and unlimited camera recording. You can add on water leak sensors, glass breaking sensors, CO2 detectors, etc.
Abode is the best deal for an integrated, affordable DIY smart home and security system. Its Gateway (2nd gen) will benefit most homeowners and Iota all-in-one will be a good fit for renters. Both options come with no contracts, no required monthly fees, Alexa integration, and Zigbee and Z-wave compatibility. Also, the extra feature to add short-term monitoring for vacations is unique for a professionally monitored system.
Vivint is an all-in-one smart home solution. A professional will install window and door sensors, glass breaking sensors, CO2 sensors, motion sensors, garage door sensors etc. The best Vivint feature is the silent alarm. For example, if the intruder asks you to disarm the system, you can fake it and alert Vivint instead.