You want to ask iOS to send accelerometer data to your application.

Use the startAccelerometerUpdatesToQueue:withHandler: instance method of CMMotionManager. Here is the header file of a view controller that utilizes CMMotionManager to get accelerometer updates:

#import <UIKit/UIKit.h>
#import <CoreMotion/CoreMotion.h>

@interface Retrieving_Accelerometer_DataViewController : UIViewController

@property (nonatomic, strong) CMMotionManager *motionManager;

@end

We will now implement our view controller and take advantage of the startAccelerometerUpdatesToQueue:withHandler: method of the CMMotionManager class:

#import "Retrieving_Accelerometer_DataViewController.h"

@implementation Retrieving_Accelerometer_DataViewController

@synthesize motionManager;

- (void)viewDidLoad{
  [super viewDidLoad];

  self.motionManager = [[CMMotionManager alloc] init];

  if ([self.motionManager isAccelerometerAvailable]){
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    [self.motionManager
     startAccelerometerUpdatesToQueue:queue
     withHandler:^(CMAccelerometerData *accelerometerData, NSError *error) {
       NSLog(@"X = %.04f, Y = %.04f, Z = %.04f",
             accelerometerData.acceleration.x,
             accelerometerData.acceleration.y,
             accelerometerData.acceleration.z);
     }];
  } else {
    NSLog(@"Accelerometer is ....