Get Mac OS X system idle time in Swift or Objective-C

SystemIdleTime.m

//
//  Created by Dariusz Rybicki on 17/04/16.
//  Copyright © 2016 Darrarski. All rights reserved.
//

#import <Foundation/Foundation.h>

/**
 Returns number of seconds since system became idle
 
 @return `double` System idle time in seconds or -1 when unable to retrieve it
 */
double SystemIdleTime(void) {
    double idleSeconds = -1;
    io_iterator_t iter = 0;
    if (IOServiceGetMatchingServices(kIOMasterPortDefault, IOServiceMatching("IOHIDSystem"), &iter) == KERN_SUCCESS) {
        io_registry_entry_t entry = IOIteratorNext(iter);
        if (entry) {
            CFMutableDictionaryRef dict = NULL;
            kern_return_t status;
            status = IORegistryEntryCreateCFProperties(entry, &dict, kCFAllocatorDefault, 0);
            if (status == KERN_SUCCESS) {
                CFNumberRef obj = CFDictionaryGetValue(dict, CFSTR("HIDIdleTime"));
                if (obj) {
                    int64_t nanoseconds = 0;
                    if (CFNumberGetValue(obj, kCFNumberSInt64Type, &nanoseconds)) {
                        idleSeconds = (double) nanoseconds / NSEC_PER_SEC;
                    }
                }
                CFRelease(dict);
            }
            IOObjectRelease(entry);
        }
        IOObjectRelease(iter);
    }
    return idleSeconds;
}

SystemIdleTime.swift

//
//  Created by Dariusz Rybicki on 17/04/16.
//  Copyright © 2016 Darrarski. All rights reserved.
//

import Foundation

/**
 Returns number of seconds since system became idle
 
 returns: `Double?`: System idle time in seconds or nil when unable to retrieve it
 */
public func SystemIdleTime() -> Double? {
    var iterator: io_iterator_t = 0
    defer { IOObjectRelease(iterator) }
    guard IOServiceGetMatchingServices(kIOMasterPortDefault, IOServiceMatching("IOHIDSystem"), &iterator) == KERN_SUCCESS else { return nil }
    
    let entry: io_registry_entry_t = IOIteratorNext(iterator)
    defer { IOObjectRelease(entry) }
    guard entry != 0 else { return nil }
    
    var unmanagedDict: Unmanaged<CFMutableDictionaryRef>? = nil
    defer { unmanagedDict?.release() }
    guard IORegistryEntryCreateCFProperties(entry, &unmanagedDict, kCFAllocatorDefault, 0) == KERN_SUCCESS else { return nil }
    guard let dict = unmanagedDict?.takeUnretainedValue() else { return nil }
    
    let key: CFString = "HIDIdleTime"
    let value = CFDictionaryGetValue(dict, unsafeAddressOf(key))
    let number: CFNumberRef = unsafeBitCast(value, CFNumberRef.self)
    var nanoseconds: Int64 = 0
    guard CFNumberGetValue(number, CFNumberType.SInt64Type, &nanoseconds) else { return nil }
    let interval = Double(nanoseconds) / Double(NSEC_PER_SEC)
    
    return interval
}

@gbbr here is swift 3 version

public func SystemIdleTime() -> Double? {
var iterator: io_iterator_t = 0
defer { IOObjectRelease(iterator) }
guard IOServiceGetMatchingServices(kIOMasterPortDefault, IOServiceMatching("IOHIDSystem"), &iterator) == KERN_SUCCESS else { 
  return nil }    

let entry: io_registry_entry_t = IOIteratorNext(iterator)
defer { IOObjectRelease(entry) }
guard entry != 0 else { return nil }

var unmanagedDict: Unmanaged<CFMutableDictionary>? = nil
defer { unmanagedDict?.release() }
guard IORegistryEntryCreateCFProperties(entry, &unmanagedDict, kCFAllocatorDefault, 0) == KERN_SUCCESS else { return nil }
guard let dict = unmanagedDict?.takeUnretainedValue() else { return nil }

let key: CFString = "HIDIdleTime" as CFString
let value = CFDictionaryGetValue(dict, Unmanaged.passUnretained(key).toOpaque())
let number: CFNumber = unsafeBitCast(value, to: CFNumber.self)
var nanoseconds: Int64 = 0
guard CFNumberGetValue(number, CFNumberType.sInt64Type, &nanoseconds) else { return nil }
let interval = Double(nanoseconds) / Double(NSEC_PER_SEC)

return interval
}