National Liquidation via Amazon offers Prime members the SAM Security C5 Self-Activated Monitoring System for $13.94 with free shipping. (Non-Prime members can spend $35 or more to qualify for free shipping; otherwise, shipping adds $6.49.) That's the lowest total price we could find by $23. This system allows you to monitor your home with your cell phone. (It includes a $25 pre-paid T-Mobile SIM card.)

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