#import <Cocoa/Cocoa.h>

// register for keys throughout the device...

[NSEvent addGlobalMonitorForEventsMatchingMask:NSKeyDownMask handler:^(struct NSEvent *event){

NSString *chars = [[event characters] lowercaseString];

unichar character = [chars characterAtIndex:0];

NSLog(@"keydown globally! Which key? This key: %c", character);

}];

Возможно struct надо будет убрать.