In case of emergency, as in life or limb type emergency, your best tool is a PLB. A PLB, Personal Locator Beacon is similar to the Emergency Position Indicating Radio Beacon used on aircraft and ships. The PLB's are smaller, easy enough to carry one in your pocket.
A PLB, when triggered by the user, will send your GPS location to a satellite, which in turn, sends it down to a "Rescue Coordination Center". The ID of your PLB will indicate who it belongs to, along with some basic contact information. That data, with the location, is used to send rescuers direct to you.
A basic PLB will run you just over $200 bucks and will work just about anywhere on the planet. Cheap insurance and gets the right people on their way. It doesn't rely on cellular towers. There is no charge for the service, you only pay for the device and battery replacements every 5 years (must be done by a shop).
Another option is the Spot! type units. Basically they are similar to a PLB, but it's a subscription based service. It'll notify them that you are in trouble and need help. They also have a "check in" function that will allow you to send an "I'm OK" type message to a list of e-mail addresses you control.
Cost is a bit over $100, but you'll pay monthly or annual fees for the service.
A higher end solution is a satellite phone. Expensive, more than $1000 for a new one, plus figure on $50-$60 a month for service with no minutes. Each minute of air time is around $1.40. You cannot call 911 from these, so you'll need to know the 10 digit number for the Public Safety Answering Point (911 center) that covers the area you are in.
There are some other solutions, but these are the most common. They work well, require no licensing and can be used by anyone.
Two way radios can certainly be used, but relying on a stranger to answer when you need help is a big "if". CB, Amateur Radio, GMRS, etc. are all going to have this issue. There's no guarantee someone will answer.
And I would certainly not rely on a portable CB radio to reach out 10 miles. Atmospheric conditions, topography, etc. can all impact coverage.
If you are looking for emergency response, the PLB's or Satellite Phone are the only real answers.