LONDON, Dec 8 (Reuters Breakingviews) - Securitas (SECUb.ST) has driven another nail into the coffin of the humble security guard. The $5 billion Swedish group said on Wednesday it was buying the alarms business of U.S. power-tools company Stanley Black & Decker (SWK.N) for $3.2 billion. The deal more than doubles Securitas’ annual revenue from electronic security to $3 billion, roughly a quarter of total sales. With its higher margins and better growth prospects, Chief Executive Magnus Ahlqvist’s pivot from man to machine is a smart one, which comes at a just about acceptable price. Based on a roughly 8.5% operating margin and $50 million of hoped-for annual synergies, Ahlqvist’s acquisition should deliver $154 million of profit after deducting U.S. corporation tax at 21%. That represents a 4.8% return on investment, a shade above the average cost of capital that NYU Stern estimates for the sector. The man armed with a clipboard at the entrance to Ahlqvist’s Stockholm headquarters may not approve. But his shareholders should. (By Ed Cropley)Follow @Breakingviews on Twitter Capital Calls - More concise insights on global finance: Evaluating a retiring pandemic CEO read more Microsoft takes antitrust shot from EU AT&T’s regulatory déjà vu