Do I need a burglar alarm for my bungalow

There is no legal requirement, and no planning permission needed in almost every case. Whether an alarm is worth it comes down to your insurance and your layout — and a bungalow's layout does change the maths.
On a two-storey house, bedrooms and half the windows sit out of easy reach. On a bungalow every door and window is at ground level, so there is no upper floor to fall back on, and the bigger plots bungalows often sit on tend to come with side access and mature planting that gives someone cover to work. The practical consequence is cost: a bungalow needs more door contacts and sensors than its bedroom count suggests, so it prices closer to a larger house than a same-sized flat.
Check your policy before you buy anything. An alarm is rarely mandatory, but some insurers require one for higher-value contents or in certain postcodes — and if you declare an alarm, you have to actually set it, or a claim can be refused.
Then decide what you want it to do. Bells-only is a visible deterrent at £500-800 installed with no monthly cost, but nobody is alerted while you are out. Monitored runs to about £1,100 installed plus £15-40 a month, and police response additionally needs a confirmed system, an NSI or SSAIB-certified installer and a one-off ~£50 URN fee.
One thing first, though: good locks, exterior lighting and a lockable side gate stop more opportunist break-ins per pound spent than any alarm does. On a bungalow the side gate matters more than most people think.
Full breakdown of what systems cost: burglar alarm costs. When you are ready to price it up, get free quotes — and ask each installer for their NSI or SSAIB certification number if you want the option of police response later.