Agents are warned that they may not be compliant if they simply press the “test button” on carbon monoxide alarms.

The law, which came in on October 1, requires the testing of smoke and carbon monoxide alarms at the start of each new tenancy.

But an expert has warned that simply pressing the test button on a carbon monoxide alarm is not sufficient to ensure that the alarm is working.

The test button simply tests the circuit, but does not check whether the sensor is working.

The new Regulations, however, specifically require landlords to ensure that there are “working carbon monoxide alarms”.

Agents carrying out this duty, including those who delegate it to maintenance staff or inventory clerks, could leave landlords exposed if they do not specifically check that the alarms actually work.

John Stones, managing director of Gas Safe Europe, said: “Simply pressing the so-called test button only tests the battery, buzzer and circuit, yet the sensor is the component most likely to fail.”

He said testing can only be done by injecting test gas, for example Detectagas, over the alarm.

Agents should also be aware that sensors inside carbon monoxide alarms have very limited life spans.

From October 1, private landlords have been legally required to install smoke alarms on every floor, and carbon monoxide alarms in rooms where there are solid fuel appliances. This requirement applies to properties with both new and existing tenancies.

The new law applies only in England. But does it go far enough?

For example, why aren’t carbon monoxide alarms required where there are gas boilers? The new Regulations require only that they are fitted into a room used as living accommodation and which contains a solid fuel burning combustion appliance.

In Northern Ireland, the legal requirement to have carbon monoxide alarms fitted is much wider than in England, under Building Regulations in force since 2012, but arguably still not wide enough.

If you listened to Radio 4’s You and Yours programme yesterday, you will have heard an impassioned plea from a mother for the law to encompass all homes, both old and new and whether rental or owner-occupied.

Stacey Rodgers lost her only child, ten-year old Dominic, in February 2004.

He died because a neighour’s faulty boiler leaked lethal carbon monoxide through the brickwork and into his bedroom. He would probably have died within five minutes.

Stacey has since been come a passionate campaigner to raise awareness of the dangers of carbon monoxide poisoning.

As she said on the programme yesterday: “Your own property might be okay, but what about the home next door?”

Incidentally, while Northern Ireland is ahead of England, and Scotland is due to have its own legislation on alarms in December, in Wales, alarms are recommended but not mandatory.

It seems that it often takes a tragedy before there is action.

In Northern Ireland, carbon monoxide alarms became mandatory in all new homes, whether rented or owner-occupied, and also whenever a boiler or solid fuel stove is upgraded, after the deaths of two teenagers.

Yesterday’s programme also looked into the likely widespread ignorance of landlords in England to install smoke and carbon monoxide alarms.

Housing analyst Kate Faulkner said that landlords who did not belong to an accreditation or membership body, or who did not use an ARLA, NALS or RICS agent, were all likely to be in the dark.

Stacey’s story is here