Out for dinner on an overseas business trip thousands of miles from the UK, Isobel answered the call on her mobile expecting to speak to her children. Instead, she heard the voice of her estranged husband, whom she was in the process of divorcing after years of violence in which she had been punched, kicked, strangled, pulled around by her hair and thrown down the stairs.

“Before the children came on the line, he told me exactly where I was – which city, in which country, and which restaurant I was sitting in,” she says. “I was absolutely beside myself. I was just so overwhelmed with fear, wondering how the hell he could pinpoint me like this. I asked how he knew and he said: ‘I can find you on your iPhone.’”

Mark had bought the phone for Isobel, who is in her 40s, and set it up before she left him. It seems likely he was using the geolocation services built into all smartphones; if you know, or can guess, the password to someone’s cloud account, you can follow their movements constantly via the software designed to find lost or stolen phones that comes installed on many devices.

That isn’t all a smartphone offers if you want to monitor someone’s activity. Spyware allows you to listen in to and record calls, read texts, see photos and even watch your subject via their phone’s camera. Last week, Catharine Higginson, a 45-year-old teacher from Surrey, revealed how her husband James had been tracking her texts and conversations via an app on her phone. She was initially shocked, she said, but didn’t see it as spying – instead interpreting James’s actions as a mark of his concern for her wellbeing.

Higginson may be happy with her lot, but there are growing numbers of women, like Isobel, for whom the opportunities offered by smartphones for tracking and surveillance are nothing short of terrifying. Abusers are increasingly using this technology, say domestic violence charities. “For women experiencing domestic violence, these technologies can be used to further terrorise and intimidate them,” says Sandra Horley, the chief executive of Refuge. “Online tools and mobile technologies can provide yet another way for perpetrators to exert power and control over women.” A Women’s Aid survey found that 41% of respondents’ partners or ex-partners used their online activities to track them.

Refuges, whose locations are kept closely guarded for the safety of their users, now often warn women fleeing abuse to check their phones for apps that might be spyware, and to switch off location services before they arrive. Tracey Noble, refuge manager for The Dash (Domestic Abuse Stops Here) Charity in east Berkshire and south Buckinghamshire, has seen at least three women in the past year who came from other refuges because they had been found there by their abusers via their phones. They have helped a woman who had been traced at three previous refuges.

New technology is being developed so quickly, and social media pervades so many aspects of our lives, that it is hard to stay ahead, says Jennifer Perry, the chief executive of the Digital Trust, which supports victims of digital abuse. In fact, spyware, she reckons, is “yesterday’s technology” for tracking victims: “The easiest thing is to access the woman in the cloud. A man might buy a phone and set it up for his partner to be ‘helpful’. He knows the username and password. You have women who don’t even realise they have a cloud account in their smartphone.

“There is also an app you can buy that mirrors the phone on to a PC. The man can just sit at his computer and watch everything that happens on the phone.”

The technology is cheap and accessible, she says. And evading it is often not as simple as just turning the phone off. Perry usually advises women to take their sim card out, leave the phone with a friend until it can be cleaned, and use a cheap pay-as-you-go device in the meantime. But if her ex-partner owns the phone, it will never be safe.

Cloud storage is particularly problematic because it is linked to laptops and PCs, which, unlike phones, can have spyware installed on them remotely via email. “You often find that a woman had spyware put on to her computer remotely, so even if she changes the username and password for the cloud on her phone, the abuser can see that on the computer and get back in,” Perry says.

Perpetrators don’t just use this technology to find out where an escaping partner has gone; it is another tool for abuse when they’re together, too. “They will use the information to belittle or threaten the woman,” says Clare Laxton, public policy manager at Women’s Aid. “They’ll say: ‘Why were you at this restaurant? You’re cheating on me, I’m going to kill myself.’ It closes down that woman’s space, so she won’t want to go out and socialise, because she knows the abuse she’ll get when she gets home isn’t worth it. It’s all part of controlling her as much as possible.”

Laxton believes the new offence of coercive and controlling behaviour being introduced by the home secretary, Theresa May, will be important for policing such patterns of abuse. “These sorts of behaviours are exactly what it is aiming to capture,” she says.

Fiona, 37, says her ex-husband somehow managed to get all her emails to appear on his phone during their relationship. When she asked him to leave after eight years of abuse, he followed her with a video camera, repeatedly broke into her house when she was out and confronted her with “evidence” when she started seeing someone else.

A friend advised her to check her phone, and her ex admitted he had been tracking her using location services. “He could see where I was to within a metre,” she says. “I didn’t even realise that was possible. It’s a really horrible feeling to think that someone who has been violent towards you, who absolutely hates you, knows exactly where you are.

“My ex-husband was a local businessman whose image was important to him; he was not going to do something overt. This technology gives people like him such a huge toolbox to intimidate their victims.”

The police investigated the violence Isobel suffered, but the CPS decided not to prosecute, saying the fact that she had started divorce proceedings meant securing a conviction would be hard. The prosecutor’s fear, the police explained to her, was that the case would look like a “messy divorce”.

When she and her children had moved to a new address that was kept secret from her ex-husband, he left an iPod for them at their school. It was linked to his computer and all the location services were enabled. Isobel opened it at the school, but was devastated to think he could have found out where they were.

Mark still sends devices such as tablets to his children, and the tracking is always on. “I get them all wiped,” says Isobel, who has been supported by Refuge. “It’s sad for the kids, because sometimes there are things on there that he’s paid for that they want, but it’s too much of a risk.”

But knowing how to deal with the practical side of the technology doesn’t lessen the psychological impact. “I feel like I’m some sort of crazy woman who is totally paranoid, and that’s not how I normally conduct my life,” Isobel says. “I’m a rational, sane person, but that is taken away from me, along with my freedom to be myself, and be the parent I want to be. I feel trapped.”

• Names in this article have been changed.