How to Send Live Sensor Data to iOS Custom Apps with BLE
I would expect this to be pretty straight forward. Off hand, I can't think of anything that would be a major roadblock to creating your iOS apps. It seems like there are two problems you'll need to solve:


Finding a BLE chip that is relatively easy to integrate with an Arduino, and
Selecting the tools that you'll use on the iOS side to develop your app.


Since I haven't done this my self, I started off looking on the Arduino side – mostly because it seemed like the problems there would be larger. I searched on Google using the terms:

aruduino ble

I found quite a few candidates that look promising, here are some of the better ones:


Bluefruit LE - Bluetooth Low Energy (BLE 4.0) - nRF8001 Breakout - v1.0 – I put this one on the top of my list because the price is pretty reasonable (&lt; $20 US) and Adafruit tends to do a good job of supporting their products with tutorials and at least a basic library that demonstrates the functionality of the device.
Redbear Labs - I don't know anything about Redbear, but they do well in Google searches and appear to have several products, including a BLE shield, that might do what you want.
BLEduino - this is a Kickstarter, and while it looks interesting, a very quick investigation didn't reveal a source where you can buy one.


The choice of devices will partly depend on what your ultimate goal is. Something like the BLEduino will give you an all-in-one package to build your project around. The downside of this is that you may be spending money on functionality that you don't need/want to duplicate. A breakout board like the Bluefruit LE gives you a smaller device and possibly more flexibility at the expense a bit more work to get up and running.

Next you'll need to select development tools. I started by searching with the terms:

ble swift ios

I got a number of promising results, including:


Arduino Tutorial: Integrating Bluetooth LE and iOS with Swift
Apple: Bluetooth for Developers
Adafruit - Introduction to Bluetooth Low Energy


These first three look like good starting points for "getting your bearings," the following two are specific to actual boards.


Getting Started with the nRF8001 Bluefruit LE Breakout
RedBearLab/iOS