So, if you haven't already secured your investment property, you should certainly do so after it has been renovated and before you place it on the market. Ask any investor who has done several deals, and most will tell you stories of how people have broke in and vandalized or stolen piping. A vacant home is a target for criminals!
I'm currently using the Frontpoint Alarm system. The reason why I chose Frontpoint is because their system is completely wireless (no professional installation needed), portable (you can literally move it around from house to house as you complete deals) and affordable (the package that I get includes all the equipment for $99 and $45/mo (3 year contract) for monitoring).
Now there's a cheaper monthly option that you can get for $35/mo but that doesn't include access to the Front Point mobile app, which is really convenient and allows you to arm and disarm your system remotely. Thats priceless if you have contractors or potential buyers coming in and out of the house.
The best thing is that after ordering, Frontpoint offers next day express shipping.
The system definitely provides the peace of mind that it takes for you to sleep well at night while your property is being rehabbed or on the market. Only requirement is that you need to have electricity at your property.
Do your research and if you find that Frontpoint fits your needs, send me a message and I'll put you in touch with my salesperson. As an incentive we will both get a free month of monitoring.