Actually, there are procedures in place with ATC for determining whether or not the alarms are real. They do happen sometimes and generally don't result in diversions. Someone said this plane continued to squawk 7500 - the hijack code - so that's likely what led to the decision to force it to land. ATC likely asked the pilots to confirm, they negated, but continued to squawk 7500, leaving ATC to believe they were possibly being hijacked.