Goods should be of satisfactory quality, fit for the purpose, and should be as description. Goods sold must be 'conform to contract' fit for the quality and satisfactory for the intended use of customer. They should be durable, safe, devoid of minor defects. (Sale of Goods act, 1979, Supply of Goods Act, 1982, The Sale and Supply of Goods to Consumers Regulations, 2002).
Under Consumer Protection Act 1987, or under common law, despite there being no contractual relationship between Mary and manufacturer she would be able to pursue the manufacturer for negligence while manufacturing and endangering her life. Also she could pursue the retailer, or breach of contract under SGA.
All the guarantees are legally binding and will stand in a Court of Law. But the clause that any further injury or damage caused by their faulty goods would not be entertained by them will not stand in a court of law. They might have written that for their own protection; it need not necessarily be a legal verdict. In this case the alarm has caused extensive damage within a day and Mary can prove that she was not at fault and did not misuse the alarm in any way. Hence, the protection clause the retailer will not protect him because it will be read as unfair contract terms and thus, will have no legal standing.