This is one of those things you've probably never though about but most likely should. Because standing between your computer and all your connected stuff is a little blinking vampire that most likely is costing you money.

Presenting: The cable modem.

That's the little thing with three or four lights that sends the GBs to your Wifis and lets you do all the things. And there's a pretty good chance that you're shelling out money for it every month. Money that could be used to, say, buy a cable modem instead.

The decision is easy. Mostly.

First, find out how much your internet service provider is charging to rent a cable modem every month. The easiest way to do that is to look on your bill. Or maybe you'll need to give 'em a call.

Comcast — America's largest ISP — by example, charges $10 a month — plus taxes and fees — to rent a modem. The No. 2 ISP, Charter's Spectrum service, gives out a modem for free. So it'll definitely vary by service.

This is basic math, folks. If renting costs more than purchasing, then you should probably buy outright.

But let's go back to the Comcast example, since the math is nice and neat. We'll assume an extra $2 a month in taxes and fees, for a nice round $12 a month for the privilege of having the hardware necessary to use the internet that you're paying for in the first place. That's $144 a year.

If you want a purchase a modem outright, though, it's easy enough to do. You may be able to just buy one from your ISP and save a trip. Or if you prefer the online route, the Netgear CM500 cable modem — one of the higher rated ones out there, but there most certainly are others — is just $53 on Amazon. (Just be sure to check your ISP's website to make sure you're buying a compatible modem.)

That math is pretty darn simple. In our example you're spending almost three times as much to rent a modem than if you were to buy one yourself. And that's if you were to only keep your purchased modem for one year. The longer it works, the more you'll save.

Are there any reason to rent? Sure. Mostly, laziness.

Caring for a cable modem isn't exactly difficult. Ninety-nine percent of the time it just sits there, dutifully blinking away. But when things go wrong is where renting might actually be advantageous.

For one, renting a cable modem means your ISP is on the hook to replace it should it die, or update it should that need arise. Basically, you're paying extra to avoid the hassle of worrying about it. On the other hand, if something does go wrong you're going to be inconvenienced whether or not you bought the modem yourself.

So the questions you have to ask yourself are:

  1. Do you like wasting money on renting things you could purchase instead?
  2. Do you want to deal with replacing or updating your modem yourself?

Just do a little homework, and do a little math, and save yourself a little dough.